I am not as advanced as many players on here so I really really depend on hitting a heavy ball on ground strokes and serve to win.
I personally can describe how I do it, and did not even understand what I was doing until my hitting partner told me and started yelling at me and themselves as they thought they were miss hitting.
I just really dig in and spin it forward no up and cut and fallow through as much as possible.
As for serve I really don't know how I hit a heavy serve but it is all I've got, as I can't hit any other serve not even flat

I feel really ashamed about that.
Also have you ever been hit a rock, where the ball is so heavy (so much forward spin) that it just dies in your string bed and is unreturnable unless hitting full throttle?