Don’t want to cover old ground.

Don’t speak unless you can improve on the silence.

Don’t bet more than you can afford to lose.

Don’t spoil the ship for a ha’pworth of tar.

Don’t bite the hand that feeds you.

Don’t try to teach your Grandma to suck eggs.

Don’t bite off more than you can chew.

Don’t upset the apple-cart.

Don’t change horses in midstream.

Don’t waste too many stones on one bird.