With Smash, and many other competitive games, you gotta be a little unpredictable. If you ever catch yourself doing the same thing over and over and over and it's never working, try a new approach.

Other tips:
Learn everything you can about your main (fast attacks, things that can kill easily, etc.)
Stop rolling so much, good players will know how to punish that easily.

Also, Jiggs is so fun to play, that reaction everyone has when I land rest is so satisfying