Look before you leap - When you advice someone to thing about the possible difficulties that they might face after doing something, speaking something or doing something as such like going somewhere, talking to someone etc. you say him to look before he leaps. Well, in other words, this is an idiom which talks about the warning which you should get before doing something.
1. I advise you to look before you leap because it is quite dangerous.
2. My dog is really fierce like a hound, so before entering, look before you leap.
3. She is really strict, so I don't go to attend her tuitions, I'd advise you too to look before you leap.