As has been said above, don't get hit. Learn how all the other characters work, what their moves are. You need to know more than your own character, you need to know the others. A major part of the game is knowing what you're up against.
Before trying to up your technical skills, start playing smart. Be patient, watch closely. Trick enemies into throwing out slow/laggy moves and then punish them for it. Marth can't do anything for a bit after his fsmash, and you can take advantage of that. Lucas's upsmash takes ages. Take advantage of it. Use your dodges, and focus on using all of the tools available to you. When I started out, I neglected my aerials and tilts a lot. I pretty much just spammed smashes. If you can't shorthop, that's one tech you should focus on first.
I think once you start using everything available to you and just get more comfortable with your character, your play will get a lot better. That's how it worked for me, at least.