I use these Runes to activate both passives from the beginning. The Magic Penetration is needed against Tanks. The extra life boost is needed at level 18 for Survivability.

First purchase a long sword and a health poison.
Then after some laning and getting Level 6 I push and then go back to base to buy the boots of speed and the Hextech-Revolver.
Next time u go back buy the boots: Boots of Swiftness against squishys or Sorcerers Shoes against Tanks. And buy some parts of the Rylais. First Blasting Wand and if u got enough money buy the Amplifying Tome or the Giants Belt.If u got some money Left buy a ward for the dragon. You need it if the other toplane champ can get trough the wall, like tryn. With the ward you can just shadow dance to him and kick his ***. When u got enough Gold go back and buy the Rylais. You can buy some Parts of Lich bane, too. When u finished Lich bane, you need to get a little bit of Survivability. For getting it just look at the enemys Team. When they only got normal dds buy the thornmail. When thy do almost only Magic damade the force of the nature. Then just finish the Hextech Gunblade. After that sell the Long Sword and buy a Rabadons Deathcap. Then u do Big Fat damage.

Best Masteries with Akali are Exhaust against normal dd top champs and flash so that she can easily escape. just flash trough a wall when u are in Twilight Shroud and Have fun.

After getting FB just go top. Try to hurt the enemy with your Mark of the Assassin. When u got level 6 and u have the boots of Speed and the Hextech Revolver just take the runningspeed buff. Then your enemys cant escape. Go back to Lane and level a little bit. When u got level 10 go and pwn the dragon. In Teamfights just jump in with Shadow dance, then use twilight shroud to get invisible. Always Target the enemy with the lowest life. Use ur Mark of the Assasin and do a normal hit to do tons of damage. Then the Crescent Slash and then one more autoattack if u got Lich Bane. Then wait until your skills are ready again. Then just use this combo. When he tries to get away just jump on him with Shadow Dance. Thats all u have to do.