When to make a move and other questions from a Donkey

[Hawt]

I was just wondering, in a tournament, how far short stacked do you think you need to be before you should start making some moves? For example the tournament I am in now...

Stack: largest 29575, smallest 5, average 3902
Your current position is 1799 out of 2832 (I have 1785, just lost about half my stack)
Blinds are 75/150 (roughly 12bb's)

So yeah, how far under the average stack do you think you need to be before it gets to "make a move" stage and start pushing in?

I ask this because since I am a fairly tight player, I sometimes let myself get blinded down to a point that it almost takes me out of the picture entirely. I just used this tournament I am in as an example so please feel free to elaborate on more specific things that what I listed.

On a side note: I just folded my AKs to some guy who reraised me all-in preflop and showed Aces so I am kind of proud I didn't get desperate there and just call.

Edit: Also, what do you think about playing weaker hands in the BB? If you get dealt something like KTos or A7s, etc, do you think it is a better idea to check and see if you hit (and risk being outkicked) or to raise preflop and try to push some people out?