not let the grass grow under your feet
US /nɑt lɛt ðə ɡræs ɡroʊ ˈʌndər jʊər fiːt/
UK /nɑt lɛt ðə ɡræs ɡroʊ ˈʌndər jʊər fiːt/

1.
to not delay in taking action; to act quickly and without hesitation
:
•
When the opportunity arose, she didn't let the grass grow under her feet and applied for the job immediately.
•
If you want to succeed, you must not let the grass grow under your feet; always be proactive.