I like learning new ones and use them often. Some of the one's I can think of right now"
"De tal palo, tal astilla" - like father, like son
"Cuidate que el tiro no sale por la culata" - be careful your plan doesn't backfire on you.
"A donde fueres, haz lo que vieres" - When in Rome, do as the Romans
"Al hierro caliente, batir de repetente" - Strike while the iron is hot
"Antes de que cases, mira lo que haces" - Look before you leap
"Caras vemos, corazones no sabemos" - You can't tell a book by it's cover.
"Si esta vibora te pica, no hay remedio en la botica" - You're playing with fire
"Entrada de caballo y salida de burro" - Don't start something you can't finish
"No sabes en que palo te trepas" - You don't know what you're getting into
"De dicho al hecho hay mucho trecho" - Easier said than done.