Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Make sure you have the AD rune and the Brute Force Mastery to get your passive in the beginning
Focused regularly in teamfights
Hard to master
Your primary objective is to get tons of last hits because if you don't get enough, you won't be able to get your core items soon enough to get kills. While last hitting minions, you want to put your shroud behind enemies' minions (if they're casters) or right on minions (if they're melee) and try to put a mark of the assassin and a melee hit (to toggle the magic damage) so your opponent's life is getting lower and lower, but, you don't need to kill him yet, you just want to get him low enough so you can use your Exhaust/Flash to finish him. Do this until you have around 1300~1400 gold then recall and come back asap. When you get your ult, you should try to gank mid or your own.
In the beginning of mid game, you have your Boots of Swiftness and your Giants Belt. At this point, you can chase and finish everybody, but don't try to kill someone on first hit. In fact, as Akali, you always want to hit, run, ult back on your target, ult back on creep if needed, comeback on target and also use your shroud as a cover ready to use escape route. You can engage fights with your shroud but I don't recommend doing this since you won't really be able to run out of fights then.
At this point you're pretty much the biggest threat on your team and the enemy team will try to focus you. You can easily take down everbody in 1v1 easily. For team fights, let your team engage and come in just 1-2 seconds after , always focusing squishies as usual and if they start attacking you, use your shroud as a cover.