It's the outs baby, the outs.
I think for me, it's simply what kind of action comes on the flop(1), do I have the other player/s covered (2), could I be drawing dead (3), and how many outs do I have? (4).
I despise the "big laydown", and actually take advantage of others who just love making the big laydown. However, MTT's are all about survival. If it's early and not a lot at stake, or I'm not too invested preflop, I don't mind laying down a big draw. And the more players in the pot, the worse it is. So, heres my plan, and it has saved me a few times;
I get more aggressive when my draw is backed up with top pair, a backdoor set of flush, or ie; more outs! You actually had 2 players fighting for the dumb end of the straight! Can it get any better? Actually, yes.
If I flop an open ender for a st8, but also have top pair and a back door flush or trip possibilities, I am far more willing to call/raise. That way, if someone already has a st8, I still have outs. (8 for the st8, 9 for the flush-less any flush cards that are part of the st8, 2 for trips, 3 for two pair, around 22 outs in all, yea-haw) If you can beat my 22 outs with two cards to come, and you have zero outs, well zippy, good luck!
If it's only the open end st8, forget it. Thats only 8 outs, and even if I make it, I still might have to chop. With two people in your pot, odds were really good that not only did one have the dumb end (bottom), one already had the smart end (top), or a set, at least. What else could they have with that flop?