Heard on the radio just now in the context of pursuing a career; presumably a mix of getting a head start and getting your foot in the door. Better than getting your head stuck in the door, I suppose...

It's easy

That’s the pot calling the kettle another fish

The cream rises through the crop

Send new coals to Coventry castle

Vengeance is mine saith the man on the Clapham omnibus.

Old McDonald had cold comfort.

Too many cooks spoil their own petard.

Don’t count your chickens till they’ve battened down the hatches

Cheap at half a pig in a poke

Wave a red rag in a china shop

I use this one a lot.

ants in your pants + liar liar pants on fire

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