I think he meant the techs that make up the steps of SHFFL'ing, not like 3 AT's in all of smash. Whoo boy that'd be a strange game.
Well for a suggestion of an important tech, I think even a basic understanding of DI can go a long way to keeping you alive longer in a match. Plus the basics of DI are easy enough to learn (it was the first AT that I ever learned.) there are some good threads in the melee boards here, but the basic "survival DI" goes like this: You get hit with some big attack launching you sideways? then tilt up or down on the control stick. Get launched upwards? tilt to the right or left. DI works best when you have the control stick at a 90 degree angle to the angle at which your character is launched.
If you already knew about DI, then maybe teching would be a good next AT to learn. You know how your character sometimes gets hit downwards, tumbles in the air, and hits the floor and just lies there for a moment? Teching lets you stand up almost immediately or roll away upon hitting the ground. Good teching will make it harder for opponents to combo you.
Basically, when your character is 'tumbling', tap L or R at some point during a window of about 2/3 of a second (20 frames) before you hit the ground. When you hit the ground, you will stand right back up. Don't press L or R more than once, or you won't be able to tech for the next 40 frames. Tech in place lets you stand up with a brief moment of invincibility, and involves just the tap of L or R. Tech Rolls involve using the control stick to input left or right along with L or R. Your character will immediately roll to the side when you hit the ground.