this may not be the best way to practice (i don't know if there's like something wrong with this method but it works fine for me) but i think what helped me most is physically seeing what the right time to waveland was. what i'd do is i'd go into training mode, slow it down to 1/4 speed, grab ledge, then drop down/double jump as soon as i could. then i'd see the earliest moment where i could waveland onto the stage which was where fox's body was just above the ledge. after that just look for that moment in normal time and just speed up the inputs. it takes a lot of practice to get it down consistently to the point where you can use it without worry in a tournament setting, though. i don't really prioritize it over things that i need to work on like moving as quickly as possible after wavedashing, wavedashes oos, adjusting my wd lengths, better dashdances, etc. it's fun to do but be sure to get basic stuff like shffls, aerial drift, dash dancing, wavedashing, and other movement options totally down before even bothering with invincible wavelands imo