Important things about practicing teching:
-Use taunts to make sure that you aren't crouch canceling
-You need to fly as close to the ground as possible, this means that you will almost always DI Down+Away, not Down+towards like many use for Spacie Dsmashes (it only works for it)
-To practice it, I simply taunt with the character I wanna tech with, start whatever move with my other controller and pause [before it hits], switch controllers, input tech/DI
its kind of embarrassing that no one but Ice has really started using tech's yet, it makes edgeguarding/punishing soooooooo much harder. Marth recovers onto ledge at 150% and you jump->Bair? lol free tech.
You wanna dair? I either tech or just edge cancel away the lag. Free.
Strong fsmash at 120%? No problem, tech.