All of my progress (from a low of 943 to a peak of 1445 on chess.com) was during a 2-month period late summer/fall last year where I blitzed through hundreds of tactics problems for a few hours a day to the neglect of opening, endgame, and strategy study.
Then I had to back off because of stupid other obligations (like career and people, bleh), and it has been downhill since, but I plan to return. Of course, at my low level, just learning not to put your queen on a square where the enemy's bishop is pointing can probably gain you 300 points.
For higher level players, I don't know except what de la Maza preached in his book...I just think of a guy like Tal making "unsound" moves that still crushed Botvinnik and Smyslov when they were the top players of the previous 2 decades, albeit his reign was brief, but he won the blitz title in 1988 I think and beat Kasparov in a blitz game right before he died in 1992, when his brain should have been chessically senile at the age of 56.
Anywhere from 5-min to 30-min. Also played quite a few full-length tournament games (not sure if those were as helpful though).
I see. I think I'll give that a shot aswell. Good idea. Thanks.