holes where screw fall out

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I have two related problems:

A kitchen cupboard where the hole in the plasterboard is now too big so the nail falls out. Can I do anything to make the hole smaller so I can screw the screw back in?

A simple metal non power shower shower holder - every time I screw it in to the wall the shower holder comes loose. I have used rawl plugs to drill into the wall that divides two terrace houses but it doesn't stay in place. What am I doing wrong?

Many thanks.

David