Look into trundle and olaf for the jungle. Both have great clears and can both do full clears without backing. they can destroy towers with their AS steroids. Trundle can also gank pretty hard if you get a good iceberg down. Olaf takes a lot more work to get a good gank but your axes have a really strong slow and it's pretty easy to permaslow. But their ganking power isn't why you pick them, You pick them to take towers and to take them quickly. botrk is the main item on these two for me. Gank a lane then push the tower hard if you get a kill or camp it if you get a flash.
As for mid lane
Riven, annie, malzahar, and anivia. I personally don't play riven but my duo does and it works amazingly well in most lane matchups.
Annie, malz, and anivia are amazingly strong once you learn them.
Malz: Max your e and rush a ROA then luci boots. You can keep pressure on your lane constantly as soon as you get e maxed and your roa. If you get ahead you can delete the enemy adc or mid laner damn near every time. Once you start rolling you will likely get ganked often so keep your wards up.
Annie: q start and use it for last hits only until your stun is up then poke with it. Your AA range is only surpassed by cait, level 10 trist, and kogmaw w so you can get poke down often. AA the enemy to pull the wave towards your side so you can be safer from ganks. And don't be afraid to use tibbers to zone. Annie also bursts really hard and can erase people when ahead. Just practice your q farming. Just try not to push the waves. Let the enemy push it.
Anivia: This bird is broken op if you use it right. Rush a ROA because you will need the mana. A tear is an option but it just charges so slowly for my taste unless you get a blue and athenes. Don't throw out your stun unless you're pretty sure you can hit it because mana is a problem early on. Max E always and if you hit a stun e the enemy every time. Once you hit level 6 don't use it to farm unless you have to. If the enemy gets close enough to you drop ult on top of them and hit them with an e then turn off the ult as soon as they get out of it. You will win lane damn near every time and you can destroy clumped up team fights. Just don't EVER go melee form. Stay in the back and deal massive damage cc and dot.
And most importantly keep it calm. Don't get flustered and don't expect to place high. Practice everything.