One thing to definitely keep in mind is your table image, and what people might have noted about you. For example,
If I`m checked to and I have any pair I will raise size of pot if I`m in late position.
These are the types of notes I take on people - bets when checked to, pots with TPTK, etc.
It's key to make sure you vary your play so that others don't get a good read on you. If you do this every time, people will eventually check-raise you with TPTK or even worse if they think you're bluffing.
Dorkus wrote a great article on bluffing here
which should help a whole lot more than my rambling above.
Harrington on Holdem vol's 1 and 2 are also great - I highly recommend them, especially since you play MTTs almost exclusively.