Bide your time
Definition 1 of 1
Pro Tip 1/3Patience Implied
Using the phrase suggests you're patiently awaiting a strategic moment, not just any moment. 
She bided her time before revealing the surprise.
Pro Tip 2/3Planning Involved
It hints at a plan behind the waiting, indicating a purposeful and thoughtful delay. 
He bided his time, studying the market trends, before investing.
Pro Tip 3/3Not Passive
While waiting, the person is often actively observing or preparing, not inactive. 
She's biding her time at the internship, gaining experience.