New to Xerath, looking for advice

I've always wanted to main him purely because of Scorched Earth Xerath lol

Artillery champions are pretty fun in general but I struggle with CS mainly, I'm averaging 6 CS per game as midlane but I feel that's pretty bad all things considered with how much minions go mid

I don't know when to back or whatever, I just shove the wave under the tower and back once I've poked them down enough, any advice on Xerath outside of the EWQ combo and general mid-lane advice?