careful not to do
careful not to (do something)
A warning or instruction that one proceed cautiously, in an attempt to avoid potential problems or pitfalls. I was careful not to make any noise as I crept into the house after curfew. As you plan your talk, be careful not to bore the audience with scientific terms they won't understand. This plate is very hot—be careful not to burn yourself.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
careful not to do something
using care to avoid some difficulty or difficulties. Please be careful not to discuss politics with Mr. Brown. Please be careful not to leave the house unlocked.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.