Dude simple shadow boxing will help you greatly. You should do it when ever you hve free time. It's best to do it in a large mirror, but you can always use a wall. When you punch you fist should be an inch away from the wall. You have to pretend that someone is really there. I talking about a person who is trying to evade your attacks, attack you, and moving around. Your feet or hand should always be moving. You need to practice defence while shadow boxing, preform slips, parries, ducks,and catches.
A heavy bag will be great but even when you have access to one don't stop shadowing boxing. It's a simple exercise that is easily overlook. You should make shadow boxing part of your workout and not just a warm up.