Strike while the iron is hot
Definition 1 of 1
Pro Tip 1/3Action Timing
Use when discussing taking immediate action during a favorable moment. 
Their team won the championship, so they'll strike while the iron is hot with celebrations.
Pro Tip 2/3Metaphoric Origin
Understand it originates from blacksmithing where metal is shaped when it's hot. 
I just got my driver's license, so I'll strike while the iron is hot and borrow dad's car.
Pro Tip 3/3Not Literal
Remember it's a metaphor, not advice to physically hit iron or other objects. 
She received a standing ovation, and knew to strike while the iron is hot by announcing her next project.