Tactics
Colossus generally wants to get in and throw. The main way he does that is either pushing through holes in the opponent's offense, or punching his way through with his strong hitboxes.
Learn your hitboxes and attack timings so that you can beat or trade with opponent's who actively zone.
j.HP has a property where it moves you forward slightly. This may help you advance on an opponent. The downside is the long recovery, so if you air-to-air punch someone and are still moving in, you can be thrown on the recovery. If you have meter to tech, then it's advantageous and you can start inputting as you do it so you don't miss the tech window.