First, I gessoed a board (gesso is a primer) and sanded it pretty smooth. Then I gave it a coat of titanium white to make it slippery. You could also use a lead based ground, but I don't have any and once the titanium white dried, it was nicely slippery. I just used one colour - raw umber, straight out of the tube. I had a bunch of clean brushes ready, some Q-tips, rags and plenty of time. This is a project that wants to get done in a day; it's best while the paint is still wet and can be moved around. I hardly used any odorless mineral spirits - it loosens the paint too much and things start to get out of control, so I kept the paint rather dry. I had an old tiny brush that got too decreped to use, so I chopped it off nearly at the base and now it's a handy littler scrubber. It's just a stump, but it's good for pushing paint around. I sometimes dip it in mineral spirits, wipe it, and use it to lift wet paint off an area...it's not quite an eraser, but works pretty well.
I used a variety of brushes, but kept them all pretty dry. If they were damp with mineral spirits, they lifted off paint easier than they put it down, so I had to be careful. It was enjoyable because I only had to worry about values, just the darks and lights. With no colour to worry about, I could focus on values and details. I couldn't leave it alone! Getting into that zone where you're sorta obsessed is wonderful...time just goes away!