Hello, although I'm not a "pro" or anything, I really like to play Jayce because of how versatile he is. You can build him 2 ways, tanky, and DPS. I always usually build him DPS unless your team is made up of all squishies and are in desperate need of a tank.

Standard Runes for AD champs. Nothing much here. Instead of the AD marks, you can also use armor pen, but the AD will help with last hitting and poke early game.

Standard AD masteries.

You can alternate with Q and W, or you can just simply max Q first and W after. Always max your ult last, it's useless in lane.

Jayce is very viable and was often used in tourneys, but now the meta for top is tanky champions.

Pros:
Tons of Damage
2nd best poke in the game (Nidalee)
Strong utility (E in cannon form)
Strong Burst (Q E in both forms)
Good single target disengage (E in hammer form)
Dominates the Laning Phase
Easy farming with ranged cannon form
Brings a lot to the table in teamfights

Cons:
If you build him DPS, he is very squishy and can be melted before getting his combo off
If you build him tanky, he doesn't do nearly as much damage

His jungling will work, but it's not as strong as his laning. Start with w in hammer form for the sustained damage, and then switch to cannon and use w for the attack speed boost. Then you can max your Q, W, E, and R lastly.

For ganking, lead up with a q in hammer form to close the gap and to slow them. Then, walk in front of them while they are slowed and knock them back into your teamate. Quicky switch to cannon form and get 3 quick shots from your w and they should be very low. If they flash, immediately q e to secure the kill with cannon form.

How well you can utilize Jayce's skills can determine a good Jayce from a bad Jayce.

Your basic combo:

(Cannon Form) Q-E (E-Q is too predictable) then W without AAing

(Switch to Hammer) Q-W while getting AA's off

Disengage with E

This combo works very well because your opponent can't retaliate against it and it offers a high amount of damage in a short amount of time

Before a teamfight, always try and poke the enemy down with your E-Q combo in cannon form. This will get your team a lead that could very well decide who wins the teamfight. As the frontline engages (bruisers/tanks/assassins) like Leona or Kha'Zix, stay at the back of the teamfight and play like an ADC. As the teamfight ends, switch to hammer form to finish them off.

Good luck in Soloq with op Jayce (don't tell Riot)