Permission first
Land ownership determines whether collecting is allowed at all. Private land requires the owner consent. Protected areas frequently prohibit collecting outright, and active workings are not open ground.
Getting this wrong is trespass at minimum. Ask before travelling, not on arrival.
Old workings are dangerous
Abandoned mines and quarry faces fail without warning. Loose rock, unstable adits, standing water of unknown depth and bad air are all routine hazards.
Never enter underground workings alone, and treat any tip or face as capable of moving.
Collect less than you can
Take what you will actually keep and record where it came from at the moment you take it. Locality reconstructed later is locality invented later.
Sites are finite. The collector who strips one has removed it for everyone who follows.
What to carry
Eye protection, gloves, a hard hat where anything is above you, newspaper and boxes for wrapping, a notebook, and a means of marking specimens as they come out of the ground.
The notebook is the part people forget. Locality written down at the face is data; locality remembered in the car is a guess, and it will be recorded as though it were not.