feet on the ground

have/keep both feet on the ground
have/keep one's feet on the ground (to be realistic, think about reality, be aware of problems; to have a sensible and realistic attitude to life; to think in a sensible and practical way and not have ideas or aims that will be impossible to achieve) — быть реалистичным (человеком), трезво смотреть на реальность; стоять на реальной почве, обладать здравым смыслом, быть практичным (человеком); не витать в облаках

It was a great result, but we have to keep our feet firmly on the ground. (LDOCE)

In spite of his overnight stardom he still manages to keep his feet on the ground. (OALD)

Related vocabulary:
keep in touch with reality
be realistic
get real

head in the couds
витать в облаках
[lose touch with reality]
потерять связь с реальностью