I was playing Bowser in FG and had a really hard time punishing a Samus that just kept rolling backwards to the edge of the stage and firing projectiles. I eventually won based on a lucky fsmash, but it was really hard due to Bowser's lack of safe approaches.
I switched to Falco the next match and just spammed lasers repeatedly to give my opponent a taste of their own medicine. When Samus tried to fire anything back at me, I'd reflect it. After the first KO, my opponent just SD'ed.
Moral of the story: camp them better than they can camp you.
Other than that, run up and shield is a very good option. This makes it so you don't have to approach from the air (a bad option in Smash 4). If you must approach from the air, find your least laggy options upon landing and use those exclusively. Your opponent is trying to get you to do something laggy so they can punish. Keep that in mind.
Also, do your best to punish rolls and evasive maneuvers. Smash 4 made these defensive moves very powerful, especially online with input lag, so try to use hitboxes that linger in the space where you anticipate them to be.