A bad Parappa player runs to a corner to boom box in a team game without a planned strategy.
A bad Parappa player doesn't use his air attacks and boombox to explosively attack groups.
A good Parappa learns combos that take the enemy inside the air. This makes it easier to continue your combo in FFA.
An all right Parappa will do Forward Circle, Neutral Circle, Bash Neutral Square to get about 70-85 AP. Then right after make the boom box for about 15-20 more AP. This is great for keeping control for your space, but isn't AP efficient.