Early game poke the enemy with your auto attacks but make sure you dont lose any farm!
If they had enough of the poke and want to engage on you make them pay for that with your shock blast (if you are lvl 2 or higher use your E too) and then switch to your hammer and to the same but make sure you land the auto attack because it deals a lot of damage!

Mid game you just want to farm a lot and poke your enemy down to the ground, this way you have an advantage because they are low and you got 6 skills to kill the enemy and ignite, flash if needed for kill!
If you win your lane so hard and got tower down already, go roam, gank mid sometimes, just help the mid or counter jungle.

Late game you want to poke the enemy from distance just make the enemy all low (even the tank!!! thanks to your last whisper and black cleaver) and wait till they are at 3/4 hp or 1/2 hp and then let your team engage.
When they enegage you put your E in line for your team for ultimate engage speed and shockblast right after, then switch to your hammer and Q auto attack E W the enemy AP carry or AD carry.

Hi, my name is Okillerbeast and this is my (first) guide on Mobafire.
I hope you will think this guide is usefull, took me a lot of time but if it helps you I am happy.
This is the way I think jayce should be build and played if you think different it's okay and leave a comment how you think is should build and play jayce!! ( no rage comments)

For farming just use your cannon, for the last 3 magic minions you can use E and Q to clear them out at once (on lvl 6/7 or higher).