Junglers= Alistar/Nautlius/Maoakai, Nocturne, and Shyvana.
Adc = Caitlyn, Vayne, Ezreal/Corki
Support = Sona Leona and Zyra
Solo top = Jax, Malphite, Kayle, Olaf.
Mid = Katarina, Karthus, Anivia, Evelynn.
Alistar/Nautlius/Maokai will help your lanes win. At higher levels of play these characters will be your go to for winning your teammates lanes for them. They can all level two gank, though Alistar is the king of this. Shyvana and Nocturne instead will help you counter jungle and really carry games at lower levels of play. Not to mention, they require you to really get into the enemy jungler's head and will help your other lane gameplay as you'll quickly grasp enemy jungle routes and realize just how much time you have per enemy jungle before a gank can be expected.
Caitlyn will help you counter kill lanes. You can outpoke Corki and Ezreal for hours and with Janna, Taric, or Alistar they'll never get to you and you'll just wittle them down over time. Vayne counters Ezreal who has become something of a power pick and shutting him down really helps in team fights. Corki and Ezreal are both tons of fun and have super strong early games and when coupled with Leona/Sona you can force kills pretty early and increase your farm.
Sona is a beast. I don't need to say anymore than that. She has a AOE CC, heal, buffs, and more debuffs than you can shake a stick at. Leona will help you snowball your Ezreal's and Corki's pretty hard as well, and going man mode as them is always a plus. Zyra also works for kill lanes, specifically if your ADC picks Draven her roots and slows help his axe catching dramatically.
Jax Malphite Kayle, Olaf, and Vlad (top) are perhaps four of the strongest picks in the game for top lane. They counter essentially all the top champions. Jax and Olaf really burst people down and once you start snowballing you won't stop. Malphite is an amazing counter pick and will become downright god like endgame if he's not banned. He adds CC in the form of a slow and his awesome ult which you can use for a variety of reasons Kayle helps with some of the more usual solo tops and Vlad for a double AP AOE comp. Not to bog this down, but knowing Shyv will come in incredibly useful in games you're going to play against that asshole Yorick (w, run away, run in, EQ, run out)
All of the mid picks I've detailed are amazing at a few things, mostly shoving your lane and ganking another. Kat is amazing at this and at 6 (or after you get your first time) can shove to turret and run to a lane. Make this decision early as it dictates what your first time will be if you're winning your lane. If you're going top I get a haunting guise to make me more tanky, if I'm going bottom I get sorc treads since they're squishier there and it's easier to force the kill with this item. Karthus is incredibly useful for farming and the global presence of his ult and his team fight presence can't be ignored either. Anivia has less of a global presence, but her team fighting in my opinion is even better than that of Karthus. Evelynn like Katarina also excells post 6 at shoving her lane and rushing to gank either top or bottom. As Evelynn I usually focus on feeding my ADC kills late-early game all through mid game since she can ward hop, where as Katarina I prefer to rush top since I'm A) more tanky and B) if the lane is doing well I can know where a ward is if they have one, and my top can deny their placement if playing well. As Evelynn you can also counter jungle if you're shutting your lane down hard enough through stealing the blue wraith with some quick Q's and an E (Kat can easily do this in one rotation, though burning Shunpo takes away your escape and not using it slows the kill significantly)
Another important note in ranked is what turret to push and when. If you can burst mid down, its best to break the turret down as well since it opens up their jungle more easily. If you're easily winning your lane though its more beneficial to keep the turrets up though if you scale better into late game as well. This forces anyone to be stuck in the laning phase. If losing its better to shove and break one down so your team can shove the lane to the inner turret and build up a large wave the person who is behind can either A) farm to catch up or B) allow the person carrying to farm in order to get more ahead.