From Longman Dictionary of Contemporary Englishlook before you leaplook before you leapCAREFULused to say that it is sensible to think about the possible dangers or difficulties of something before doing it → look
Examples from the Corpus
look before you leap• Proceed with caution and, at the risk of sounding like a tabloid astrologer, look before you leap.• Whatever you decide, it pays to look before you leap. 