One of the best ways I have discovered to improve oneself at Super Smash Bros. Brawl is to play in multiplayer brawl. When doing this, set one opponent to cpu. Turn the others off. Set the cpu difficulty to 5 (do this by pressing A while your cursor is over the number in the lower right corner of the cpu character). Set the cpu to random character, and play on a random stage.
Play the cpu until you beat it three times. Once you do this, increase the difficulty of the cpu and try to beat it three times on that difficulty.
Repeat that process over and over until you can defeat a level 9 cpu.
Then, put in another cpu. Set this one to level 5, and leave the other one on level 9. Do the same as before, slowly increasing the difficulty of the opposition.
Repeat this entire process until you can defeat three level 9 cpus.
When you reach that point, you might as well team the opponents together against you when you play real people. Chances are, you’ll dominate.
Rocket's Game Corner 