To get easy kills, equip your hidden blade and throw an enemy to the ground. While they are lying on the ground, stab them. This is especially useful when surrounded by enemies or when assassinating targets.
Note: Only attempt this technique if you are skilled in the Rank 2 skill "Counter" and have enough Synchronization bars; one and a half rows of bars are enough. During battle, equip your hidden blade. With this is equipped, all of your counters will score an instant kill. You can even instantly kill tougher ranked guards (such as the Teutonic guards in Acre when hunting Sebrand). Also, most of the time, using the hidden blade in battle will scare the last one or two guards, causing them to run away. However, since you do not have a weapon that is sufficient enough to block a full sized enemy blade, all incoming attacks will hurt you.
During battle, if you see a guard you are fighting physically emote in any way, press Low Profile Assassinate while facing them to score an instant kill without the need to counter.
The best weapon when facing four guards or thugs is the Short Blade.