I undercoat my bases in black and then paint them in snakebite leather.
I then cover the tops with white PVA glue and dip them into sand.
I don't bother painting the sand, despite the fact that this seems to be the standard from GW. After all I want my bases sand coloured, and whats better for that than sand!!!
When dry, I paint over them with some very watered-down PVA glue, this makes sure the sand stays in place.
The plastic models are very light and easily knocked over. To give them extra weight and the right "feel" I glue a suitably sized coin inside the bottom of the base.