You have to be ready to strike as soon as you see one. If you don't, someone else will.
This is a very sage piece of advice. So many times I see post where someone finds a really good deal and is either unwilling to spring for it without an approval from the internet community, or they have to go home and think about it. The next day it's gone because someone else came in behind them and bought it.
Do your research, BEFORE you start looking seriously. Then when you see a deal BUY it, don't dither around wringing your hands about if you can find another one for $25 less.