Spike are usually slow and quite precise to place. My advice is just to go for it. Spam it. Feel it. But check the hitbox first in training so you kinda know where it is.
You'll fail alot. SD alot. But you'll learn where you can and can't get your opponent offstage with the fatal blow. Eventually you'll see exactly when the occasional is there and surprise your enemy's stock with a one-way ticket to the void.
Spike is about read, risk and anticipation. So you won't place it every match.
Teck is kinda the same. Go to training, get near a wall and let the cpu f-smash you over and over again. When you're about ½ of a second to touch the wall, press shield or grab.
Soamming or holding is useless, you have a time to tech and a cooldown if you pressed too early.
You'll see that there's a limit when you bounce too hard and can't tech, it'll be shown with red "slams".
Then, when you know how to do it, training useless, time to battle ! You'll have to learn in the stress of battle that if in the second after you get hit, you're about to touch a wall, ground, anything, you have to PREPARE TO TECH.
This is really important to antipate where the opponant is about to throw you to see if you need to tech quickly or no. But don't anticipate too much, because you could just airdodge into the void.
Also, if you failed a tech against the "bottom" of the stage, stop pressing shield, or you'll airdodge into your doom.