How to Perform: Do a D-smash/D-air at the very beginning of your character's landing animation.
Effect: Character does a D-tilt instead of a D-smash or D-air. Timing is super-difficult, but it is possible.
*Note: On-land D-tilts can be performed without glitches by holding Down and pressing A/C-stick-Down during landings.*
In retrospect, I guess it doesn't have a practical application after all. Forget I said anything!
So buffering a d-tilt.
That's just a timing issue and you're just going to have to practice it. There is really no way to get around this. If you're having problems with a specific tech like this that is completely timing dependent, then you're best option is really just to practice it.
Now as for the original poster. I know a lot of people have been saying learn to play melee, but it really does help.
If you are having problems with
right thumb movements, learn to play Fox and practice waveshining, drill shine infinites, short hop double lasers, shffl'd aerials out of a shine, you know, stuff like this
http://www.youtube.com/watch?v=kZaEFTm1Yxs. You don't have to get 100% consistant with it, you just need to be able to actually do these actions when you really try and you'll see a noticable increase in tech skill.
If you're having problems with
left thumb movements, go with Peach and learn to Floatcancel nair->land, repeat. When you do it right it should look something like this.
http://www.youtube.com/watch?v=arMpGUoDPh4&feature=related 0:48
It requires quick and precise movements with the control stick to be able to get the float, do the nair, and fast fall as soon as possible. It's a great exercise.
So to those of you complaining about the people just saying "play melee," please realize that it really does have some merit.