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/
"not let the grass grow under your feet" picture
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.