Wavedashing: This is a difficult technique that will take a lot of practice to master. It is the easiest to do this with Luigi but trying it with many characters will prove to be more beneficial. To wavedash, you must first short hop and then air-dodge diagonally toward the ground in the direction you wish travel. If done correctly, a puff of smoke will appear around your characters feet as they slide quickly across the ground. This technique can be used repeatedly and has many possibilities such as:
Wavesmashing: While wavedashing you can charge and execute smash moves. This allows you to quickly approach another player and attack at the same time, giving your attacks more range as well as surprising your enemy.
Wavedancing: This is just wavedashing back and forth or around the level but it makes your moves unpredictable. You can also wavedash off ledges backwards to keep other players from being able to return to the level. The same thing works for platforms which can aid in quick escapes or attacks.
Wavelanding: If you are in the air you can just air-dodge at the level when you are about to land to wavedash as soon as you land.
Wavesheilding: This means that after you wavedash you can shield and slide up to or past another character.
Here is a video that I found that might help.