From Longman Dictionary of Contemporary Englishhave/keep your feet on the groundhave/keep your feet on the groundSENSIBLEto think in a sensible and practical way and not have ideas or aims that will be impossible to achieve It was a great result, but we have to keep our feet firmly on the ground. → foot
Examples from the Corpus
have/keep your feet on the ground• She's really creative, but she also has her feet firmly on the ground.• So I guess inversely he taught me the need to be prepared and keep both feet on the ground. 