His level 1 - 3 is INSANE. Sol can bully almost any champ out of getting farm. You should also be taking advantage of the fact that everyone understimates him, ff you can get your jungler to gank early, a q + w combo is enough to get first blood easily.
His E is amazing, by the way. With it, you can be a constant presence all over the map. Use it to roam, escape, recall and head back to lane without missing cs... His E is his greatest asset, so use it.You should be maxing it second, as the extra 0.4 second stun time on Q is simply not worth sacrificing a 45% movement speed bonus and 7000 range teleport.
Even if the enemy team knows where you're headed, just being a constant nuisance everywhere is invaluable. Don't be afraid to gank really early, too. You'd be surprised at how many double kills at 3 you can get just by roaming bot to an overextended lane.
Whenever I play Sol, it's all about the roam. I don't even focus on getting the mid tower. I shove the creep wave in, and then gank gank gank.
A few final tips:>Exhaust is much more useful lategame, and can help you survive ganks/assassin all-ins>Your ultimate never does as much damage as you think it will, so be careful when using it to secure kills