Wukong's W-Spell called Decoy is a very strong ability to escape from death. Anyway, it has a rather long Cooldown, so wait until you really need to use it.
Before actually using it, try just to press "S" in order to stop any movement or fighting:
The enemy will think you used "Decoy" and will not attack you. After he goes the way he thinks you would have gone while you've been "invisible", just go to the opposite direction. If he is able to catch up on you, you can still use Decoy or press "S" again. If he thinks you used Decoy again, go into the opposite direction. If he thinks you wanted to trick him again, he will attack you after you pressed "S". In case of that you just go ahead and really use your "Decoy" this time. He will still think you want to trick him and go on attacking your "Fake-Wukong".
After that combination you should be fine and secure ;)

Another way of escaping is simply to go into a brush, activate "Decoy" and turn back. Your opponent will think you headed straight, but you actually went to the opposite direction.
You could try this tactic even without using "Decoy" (works with every champion):
Go into the brush and wait until your enemy is just about to enter it too. At the point he enters you just go the way you and your opponent came from. The enemy will be confused for at least a second, which will give you a maybe decisive advantage.

Harass your enemies with combination of jumping towards them (E-Spell), hitting them with your "Q" and finally use "Decoy" (W-Spell) to prevent taking damage from the enemy champion and to confuse your enemy.