If you've just learned to wavedash, you will find it hard to incorperate into your fights, even with luigi. during matches, try to use it as much as possible, and deliberately use it for combo starting, movement, grabs, everything. You will lose matches against your friends, but it helps you remember to wavedash during battles, and eventually you can try other combos with less wavedashing (although still many with, since you're luigi). Or, just practice in versus against a human without them playing, just learning different wavedash techniques. Practice new things, and if they seem to work, try them in real matches. Also, watch videos. The pros with luigi have mastered wavedash techniques and combos.