Im level 29 now should be 30 soon. I want to try ranked as soon as possible. I think i have all positions covered pretty good but want to know who you guys think i should add. My main is diana so champs with similar playstyles would be good, im thinking about akali. Im listing champs where i play them now.

Top- Jayce, Lee Sin, Riven, Tryndamere
Jungle - Diana, Hecarim , Lee Sin, Maokai, Udyr
Mid - Diana, Ahri
Bot ADC - Ashe, Corki, Graves
Bot Supp - Janna, Nunu, Taric, Thresh

Get 5 Runepages, fill 1 for every role, this gives you a massive advantage in ranked over Bronze players, and can nearly get you to silver on it's own (with good masteries, do research)
Riven and Tryndamere make good Junglers too.

Garen (top)
Olaf (jungle, top)
Jarvan (jungle, top)

Miss Fortune
Sona

Swain mid is powerful, and you don't need a special team comp to play him
Akali requires a wall of CC tanks or powerful teamfight champs so you can clean up and snowball, and a lot of lane ganking. Akali farms most of her gold from enemy champions.

guess i should of added i have 10 rune pages, 5 of them full with tier 3 runes.

I like swain too i might try him for another mid pick.