Hi John
I agree with Animal and would just add that, wherever possible, I always try to wet-sand resin.
I tape a piece of wet&dry abrasive paper to a ceramic tile (or anything flat, that can stand water) and place it in a shallow bowl of water. The water traps the resin dust, so a mask is less important, and it also helps keep the wetndry from clogging.
To help sand parts evenly, I use a "figure of 8" pattern, reversing the direction for each pass.
Work slowly and steadily and check your progress regularly.
All the best
Rowan