Candid photography can be great fun. It allows the human to
indulge the fun of the hunt, but using a camera instead of a gun.

Mind you, candid photography can be quite dangerous if the
subject decides it doesn't want it's picture taking !

Because of this, I use a long lens.

There are very many possibilities here - as many as there are
people at least. Steer clear of the standard 'eating' and
'drinking' pictures, and go for those that others don't take.