don't jump the gun
don't jump the gun
Do not start or undertake something before it is permissible, appropriate, or advisable. The phrase alludes to starting to run in a foot race before the starting gun goes off. Henry, please don't jump the gun and send the proofs to the printer before the boss approves them. Don't jump the gun and announce our engagement before everyone gets here, OK?
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.