mettre la main à la pâte

to do a share of the actual work yourself

It's the classic image of the baker who has to knead his own dough, so it means getting stuck in and doing the actual work rather than just giving orders.

Le maire a mis la main à la pâte pour aider à nettoyer la plage après la tempête.

The mayor got hands-on and helped clean up the beach after the storm.

The 'hand' half of this goes back to the 13th century, when 'mettre la main' already meant getting stuck into something, and 'the dough' was tacked on in the 15th, borrowed from the image of a baker who has to work his own dough to get any bread.