I have seen advice here and there about 'pinching out' the growing tip
of some plants (e.g. tomatoes and peppers) to encourage lots of fruit.

I assume that 'pinching' out means 'cutting off' and if so,

a) how should it be done (e.g. would a pair of scissors do? should it
be straight or at an angle? does the end have to be treated to prevent
infection?

b) when should it be done? Is it when the first fruit appears?

c) what plants other than peppers and tomatoes does this apply to?

thanks
Ross