I'm only Level 19, but I feel like I can give some tips because I enjoy playing him and am fairly decent. I would run Runes that work, with regular AD Masteries.
First thing I learn is that Jayce is VERY mana dependent. If I run solo top and get to lane late, I generally will switch to cannon, and fire a Q through the brush in top lane. If it hits someone, and he's solo, I'll switch to Cannon and use Q again dealing *Tons of Damage* and then draw back. If it doesn't hit anyone, I'll just camp brush. Focus on last hitting during laning phase. At least at my level, I will wreck Melee champions. They come too close? Poke them with cannon auto-attacks. I like to farm in cannon form. Also remember that you don't need to always use E + Q to poke someone. If they are close enough, a regular Q will still do a decent amount of damage. Main thing is trying not to run out of mana. I tend to max my skills as follow: Q- E - Q/W - W/Q (whichever I didn't take), then max Q whenever possible, then E, then save W for last. Level up Ult whenever possible of course.
I start Boots + 3 (or 4) in S2, but I have tried Longsword + 2 and it doesn't work too bad either. Maybe start Crystal Flask + Something else? (Since it gives back HP and MP which allows you to more freely use mana).
Only use your E + Q combo when you either have enough mana to spare, if you are going in for the kill (E + Q in cannon + R + Q + E in hammer = HUGE damage). You have a great disengage with your E.
Overall, I generally take boots that correspond to whoever I'm laning against (Usually Merc or Ninja Tabi). Rush Triforce, then if I want to go Pseudo-AD, I build a Bloodthirster (like I had to do one game because I was the ADC >.>), otherwise, I build him damage with a slight focus on tanky as well.
So basically: Conserve Mana, AA for pokes. Rush Triforce
Hopefully I helped you somehow! Even though I'm only Level 19, I feel like I have at least something to share