watch one's step
• used as a warning to someone to walk or act carefully.
• "you'd better watch your step with him—he's not as innocent as he looks"
Similar:
be careful,
take care,
step carefully/cautiously,
walk carefully/cautiously,
tread carefully/cautiously,
exercise care/caution,
mind how one goes,
look out,
watch out,
watch oneself,
be wary,
be circumspect,
be chary,
take heed,
be attentive,
be on one's guard,
have/keep one's wits about one,
be on the qui vive,
