It is really hard to write another article in this forum, as all of the necessary knowledges have been covered in many great guides and analyses. The best I can do is try a summary of a specific topic.
I started playing Civ4 as a peace lover, but now I am clearly a warmonger who is "forced to win early" by the game mechanism. The game really favors a warmonger. So, please allow me to summarize my war experiences into "10 FAQS that I ask myself before declaring a war".
Q1: What do I gain from this war?
Although not every human action carries a purpose, theoretically they should. Contemporary artists paint craps because they want to paint craps to disturb you.
Every war should serve a purpose, too. For example:
– Secure a large interior of my territory
– Gain a few precious resources that I don’t own
– Kill off a great threat in the future
– Put down a warmonger that may backstab me, before it gets a chance
– Simply expanding my empire
A competent warhead should have a clear goal in mind. Not just sending out his troops to "punish a bugger". That’s what a "jerk" would do.
Q2: What do I do AFTER the war?
It never hurts to plan one, a few, or many steps further, if you have extra time before the action is due. What will I do after the war? For example:
– Continue the war on the next target, if I still have the military lead
– Call it a day and enter a massive 500-year peaceful growth period
– Give some distant territory to a weak friend to create a buffer
– Put research to 0% and let scientists to handle "Iron Working".
– Ask for peace money when my loss is enough, and let Monty continue my war.
– Remember to put culture slider back to 0%.
There are various things to think of, some big, some trivial.
Q3: Could I have allies to help me, or the enemy?
Diplomacy usually decides the war outcome. A third party can turn the tide of war completely.
Obviously, you want to have all the help you could obtain, and eliminate all the backstabs you may receive. All of the Civs that are friendly with you are possible helps, and they are usually willing to join your war after you declare it. The aggressive / fanatic ones may start the war for you if your price is right. All of the Civs that are friendly to your enemy are going to do the same for them, though.
Shouldn’t you do something to prevent that from happening? Actually, the solution is easy. You may bribe another Civ to attack your enemy’s potential ally. You may bribe your enemy’s potential ally to attack somebody else. Just to keep them busy, and they can’t be possibly helping your enemy while they need help themselves. Note that a warmonger can be anybody’s friend, so it is especially important to bribe warmongers to go after someone before your war, or simply bribe them to help you. The good thing is that the AIs aren’t very smart at bribing others to war, so you don’t have to be over-cautious.
If you have eliminated all possible helps from your enemy, you already declare the war at the "worst" situation possible, because it can’t get worse! If you are already at an advantage at this worst possible situation, then clearly you can’t lose – only to win faster by pulling in a friend.
Generally, it is a good practice to stir a world war every time you are going to war. While everybody is busy with everybody, your target losses all potential helps. I am still attacked when I am weak, but I have never been backstabbed when I am no longer weak, but vulnerable during a war. I always make muscle man show their back to me before I draw my knife.
Q4: Could I annoy my friends, or other Civs by this war?
Certainly your target is gonna hate you, but how about your friends and other neutral Civs? I have to check the relationship of my targets to other Civs. If they are at Pleased or Friendly, then certainly I will get "You declared war to our friend!" modifier. This can potentially spoil a Friendly relationship to Pleased, a Pleased to Cautious, or Cautious to Annoyed. The consequence may be very bad.
To prevent this, you can spoil their relationship first. For example, A is your target, and B is your friend. A and B are friends, too. If you ask A to attack B’s friend, C, then B is going to dislike A a little more. If that makes B Cautious to A, then you won’t get any white eye from B when you declare war on A.
The good thing is, -1 in most cases doesn’t change anything. So you don’t have to worry that much.
Some people think they should purposely annoy the enemy so they will declare war on themselves. This usually doesn’t work, as the AIs evaluates the power difference pretty much. If you are weak, you don’t have to purposely annoy them, and they will come after you. If you are powerful, no matter how many nukes you drop on their head, they swallow the fallout and tears.
Generally speaking, during a conquest it is unavoidable that eventually you will annoy all of the Civs by invading multiple Civs in the past. It is OK. Up to a point, you will be powerful enough that nobody dares to declare war on you. You can also allign your religion with them, sell them your extra resources, and give them little helps to maintain the relationship at Pleased. And, since you still make everybody busy before you draw out your knife, they still can’t help each other against you.
Q5: Could I have declared this war 100 years earlier?
My original Q5 was "Could I have avoided this war" but I found it too lame. Of course I want to war in Civ4 because it makes me win much faster! I have to be honest. 
Could I have declared this war 100 years earlier? Sometimes yes! I am such a chicken that sometimes I want to make sure everything is safe – but by waiting I might make myself less safe. The earlier I become aggressive, the more advantages I get. I don’t have to get everything prepared sometimes, because neither is my enemy. At times, I give up the past hour of gameplay, and start the war 100 years ealier. I win; I feel very happy. 
***
In the first 5 FAQs I covered the preparation/abstract aspects of war. In the next 5 FAQs I will get into some practical details.
Q6: Is my attack route fool-proof?
An attack route is the plan of army advance, where my invading stack enters the unfriendly territory, where I camp at each turn, and how I carry on my attack to the next city. A forest, a river, or a hill can all make a huge difference.
It will be the best if I have an active update of what’s happening in the enemy’s territory. For example, if I own a holy city of a religion, I will probably get an Open Border well beforehand, and spread my "professional" missionaries to my future opponent’s cities.
If I don’t have a holy city, I can simply ask for an Open border, and send out many faster, less powerful units (scouts, chariots) for a latest update. As soon as the war is declared, these scouts will be repelled from the enemy territory, so they can either have a free return ticket, or end up in nowhere.
With a significant military advantage, it is usually good to divide your huge army up, plan multiple attack routes from different entries, and devour several AIs cities all at once. However, against smarter human opponents, it is usually wise to have an invincible stack of death. When you enter an enemy’s territory, it is possible for your opponent to concentrate their counterattack and eliminate your divided invading forces with their relative mobility. That brings up the next question:
Q7: How do I deal with a counterattack stack?
If your target is not too weak, it is very likely that there will be a counterattck stack organized, and heads towards your territory. Even if your target is weak, it might still send out a few horse riders to pillage your improvements to distract you.
Do you have enough home defense to deal with a counterattack stack, even just a few horse archers? Do you have fast unit to hunt down their fast unit? Do you have spears to poke at the horses? In my experience, about 20% of my total mobilized army are actually used for homeland defense / fortify new acquired territory. In multiplayer situations this ratio will go much higher, because smarter human players concentrate their attacks.
Another very common phenomenon is to be showered by a large number of catapults when you advance into enemy territory. There is really no way to prevent this. You need to have more units in that stack to dilute the splash colleteral damage. Some people say you can split your stack, but I don’t think it is a good idea. If I am the defender, I can easily concentrate my catapult shower on half your stack, and use all of my defending forces to kill off half of your army. By the time your intact, the-other half arrives at my castle gate, my forces have returned and started healing.
Right after taking a city, it might be worthwhile waiting for the wounded troops to heal, if lots of healing is needed. An army at half of its strength is really inviting a crushing defeat.
Following the catapult bombardment, the enemy might follow up with a mixture of other spare units. You may think AI is stupid to commite suicide this way, but those counter attacks can be devastating if you don’t have a balanced stack. If you don’t have elephants/spears in your invading stack, your melee units might get slaughtered by horses. It is wise to carry a few defensive units in the same stack, just for the purpose of insurance. Plus, they can help you afterwards…
Q8: Did I forget the garrison troops?
You might be able to take the city, but you will need troops to defend it. Chance is the enemy’s culture border still enables them to take the city back in 1 turn, if your new city is not properly defended. You must know by now that good garrison troops are very different from good attack troops. Archery + Spears/Elephant are very good garrison troops; the AI love to have them, too.
One of my common mistakes is I "barely made it", so I have one very weak unit in the new city, and I don’t have any units that can move in to help. The result is usually I lose the new city and the wounded unit to a very weak counter attack force. The AIs will hunt down each one of your weak units, especially when they can get a city back in the meantime.
You don’t want to leave a portion of assault troops in each of your new cities, to weaken your invasion as you go on. It might be too late to start producing garrison troops after your war declaration.
Q9: Did I forget to move a unit somewhere?
This is more of a gameplay aspect. When a war gets big, it is easy (at least for me) to forget a few units that has been previously assigned on garrison purpose, but no longer needed. When I can locate them (through the military advisor) and pull them to the front, my battle often becomes much easier. 
Q10: Am I on my way to my next military tech lead?
Not really an FAQ – I just include this for morale boosting purpose. When you hack down archers with maceman, you should be thinking of blasting longbowman with gernadiers. When that comes true, you should be thinking of the cheerful gunpowder explosion echos made by cavalry and cannons. After that, it is probably sniping grenadiers with infatry rifles. You are always creating a military lead, because the AI never stops trying to catch up. After a certain point, you are just going to wipe out the rest of the AIs in a short period of time, if you haven’t accidently cross over the domination victory threshold.
***
May I conclude this article with a popular quote from Sun Tze:
"Knowing your enemy and yourself, you can fight 100 battles without dire danger."
The key of a war is to avoid losing. If you can smell the war not approaching your victory, then you better quit it as soon as possible. In order to smell it, you need knowledge of the situation. If you don’t suffer huge defeat, naturally over time you will get a few chances to crush the enemy. If you succeed at doing that, you win! In Civ4 the wars are much eaiser, so usually you immediately win after a little planning.
A popular misconception of this quote turns the latter part into "you can fight 100 battles without a loss." This is definitely naive. You can still lose, because there is luck, competent enemy commanders, and endless suicide bombers (catapults). However, with enough knowledge of the situation, you may lose, but you are not exhausted. You can still regroup, tell yourself there are still lots of hope, and come back for the eventual win, while your enemy feels tired and whines "What is war good for? Absolutely nothing!"