A smooth felt, as you would once have found on a 'card table'. It reduces the risk that little things that drop out don't bounce out of sight.

I ahve also learned to sweep and vaccuum the floor of the area I am working in before starting. It makes sweeping to find the little bit that gets away so much easier. To hold small parts I use empty egg cartons. The lid can be folded over and thus keep dust out if there is a while required before the thing goes back together again.