I know a lot of people have been trying to get secret form so i wanted to help you guys out. It took me about 2 hours to figure out all this stuff and complete my first secret form. and then i realized most of what i learned was on the wiki page.
Secret_Grade_TechniquesI learned the general strategy from watching a couple replays and kitaru's videos.
http://www.youtube.com/watch?v=-KJHUDaZ5ywand i made some diagrams from some secret grade games ive completed.




Some other general HINTS are:
When you get near the top, complete the staircase first, then finish the overhang. Dont try to complete 1 hole at a time.
If you use SRS rotation system, use infinite rotate to your advantage, you can create time to think or "climb" up surfaces. for instance, when you are at the very top, you can place pieces on top of the game area where they cannot be seen but will not result in a loss. A loss occurs when the next pieces is unable to spawn due to another piece blocking it.
Get as few line clears as possible to keep the pieces dropping slower. its possible to finish with only 2 line clears.
good luck!