ammomod is infinitely better than mge, use it to practice your rockets, and if you are a pocket, play dm and only use shotgun to practice that. If you are a pocket, I would recommend at least pugging medic so you understand where the heals are going, when, and why. As a roamer, take as few heals as possible, and know when to bomb. Watching povs of good players is a solid idea as well.
and with any class, practice and play