You play a lot of Leblanc, so how do you have a hard time playing her? Akali's one of the best champions to start with when wanting to learn assassins since she teaches you when you go in and when to back off, but you already play them. The biggest thing that separates LB from Akali is Akali needs to commit to a kill or she's screwed, while Leblanc has a fail safe in the form of her W and R. Also I don't know where you're taking her, but I have a lot more success with her top than mid just because you're safer up there.
I take exhaust ignite for maximum kill pressure in lane and to hunt a carry down before a teamfight starts. It also almost forces you to play back to your tower since the lack of flash should make you feel uneasy about overextending. This works well with her since her early game is so weak. Once you hit 6, you should have revolver, and then the fun happens.
Because you don't have flash, look to chunk your opponent while ALWAYS keeping one stack on your ult, engaging as their minions are behind you. In the event that the fight isn't looking good for you, you should have at least one enemy minion to ult back to as you run to the tower, spell vamping back up to a comfortable HP level.
There are those games where you just won't have a good time. Take my last Akali game for example - I laned against a Vlad and he was just kicking my ass. Sej had to come top 3 - 4 times before I was finally ahead enough to get a kill out of a 1v1, and even then, it was close each time. Once I started getting kills, I started roaming around the map and stealing taking securing kills in order to snowball. Once that happens, all you have to worry about is pinks, and getting caught in a teamfight.