I think a good serve for new players to the 3.5 level is on the ground with a medium swing speed, loose/relaxed & fluid and loopy serve. You can get that consistent and it's relatively easy to place it where you want (as you aren't swingly wildly). It's better than pushing the ball in -- which is what I see with a lot of players.
4.0 I'd suggest starting to get off the ground. But it's difficult as you need to make sure you strengthen your shoulders and body. I've seen too many people throw out their shoulders/arms trying to serve that way (pushing off the ground).