Early Game
[*] Do NOT waste energy poking with your Q until about level 5. It is much more useful to farm creeps.
[*] Using W to try and zone enemy champions works quite well, but make sure that their jungler is not in the area, as it would make you a much more vulnerable gank target.
[*] TRUST IN THE SHROUD! If you are hiding in the shroud with enemies right on top of you who can't see you, then SIT TIGHT. Wait for a good opening to escape, and be creative. Running straight towards your turret is predictable.
[*] WAIT FOR ULT CHARGES before you go to kill someone. Not only does having one charge mean less damage, but it also means no way to escape, which brings me to my next point.
[*] Your ultimate is as much of an escape tool as it is a damage tool. Jumping to enemy minions can help you get out of a bad situation
Mid Game
[*] Here is when you should start roaming if you are ahead. It boosts your team up as well as getting you those coins.
[*] Other than look for good opportunities, there's nothing really to say about mid game. Just farm up some coins and kills and prepare yourself for late game.
Late Game
[*] THIS is your time to shine. With a lot if not all of your items, you are essentially a beast.
Here are some things to remember, though:
1. NEVER initiate teamfights. You are a glass cannon. They could burst you down quickly and then your team will be at a severe disadvantage.
2. Target the squishy damage dealers.
3. For escaping, your W acts as a slow as well, so you can help your team escape.
4. ALWAYS DEAL DAMAGE. Your AP with your spellvamp just heals you up for a TON, so don't be afraid to go HAM.

Well, that's all I got for you now. If you'd like a more comprehensive guide on Akali, please feal free to let me know.

Thanks for reading,
Raeu