The lights are on
Here are some nice tips for fighting in Assassin's Creed 2. It won't work flawlessly, but it gives you a good idea of what to do if you're in doubt.
if you face several enemies at once, you need to take into account several things: the number of enemies, the type of enemies, and the tricks you have. if you just face two grunts and you have double hidden blades, you're okay. if all you have is one blade and you face several armored brutes, you'll have problems.
making extensive use of the combat system is a good thing. disarm an enemy, then kill him. if you can grab an enemy, than throwing him into water or off of a building will kill him nicely. if you don't have any of these, you should throw him into another enemy, making them both easy pickings. when fighting a lot of enemies, switch from one to the other, so they don't get a combo off.
if you have smoke bombs and are facing multiple enemies, throw the smoke bomb and start killing them off while they're stunned. if there are too many to kill during the duration of the smoke, just run away into a lake or a bale of hay. picking up enemy weapons isint too great of an idea, but it'll work in a pinch.
that's all i have for now