Just a few suggestions with Celluclay (I've used it a lot for my bases.):
1. Get an empty Coolwhip or similar container, and put in about 1/3 or so cup of water. I always just eyeball it... To that add about 2 or so tablespoons of white glue and mix well. Now's the time to add the base ground color. I like to use Liquitex acrylics because of their high solids content. Choose your color(s) and add several drops of Liquitex into the mix, andf MIX WELL. Burnt umber and raw sienna are two of my favorites.
2. Add Celluclay. You should add more than what it looks like the liquid can support. For bases, Celluclay should be mixed as dry as possible. Stir the Celluclay into the liquid (use your hands--wear gloves) or use an old spoon. Make sure to mix well so that the base color is consistent throughout. If it looks like the Celluclay isn't all going to get wet, add just a LITTLE water. When you're done, the clay should have the consistency of fairly dry cookie dough. It should NOT be sopping wet, or look like you could get water out if you were able to wring it out.
3. Prep your base (This should be done before mixing Celluclay.) This is important. If you use a pine or other soft wood base, make sure you seal it well (Varnish or polyurethane--Minwax and Deft makes some good stuff.) or your base will warp severely (been there; done that; have the t-shirt) from the absorbed water. Next, give the base some "tooth" to hold the clay. I use some old window screen cut to shape and stapled to the base. Even then soft woods may still warp. I personally like to use oak or plywood for my bases--especially if they're going to be covered with clay.
4. Apply the clay. The clay should be applied thinly--just enough to cover the screen adequately. Applying too thick will cause undue shrinkage, and may also cause your board to warp. Use a wet finger to smooth out the clay as you apply it. I usually put a cup of water in front of me while I put the stuff down.
5. Allow the celluclay to dry before putting more clay on your base. If you want to put in larger hills or other "rough" terrain, use foam as a former instead of using lots of celluclay. Cut the foam to shape, glue it to your base, and cover with clay.
6. After you have the clay down, run a bead of white glue around the edges of the clay to help keep it from lifting off the board when dry. Now's also a good time to position your vehicle and to put in any vehicular "tracks" that you want. Simply take your vehicle and dip the wheels, tracks etc. into the celluclay repeatedly along its path to form the tracks.
7. Wait until the celluclay is dry to permanently mount your vehicle(s). I mounted mine wet once, and had the finest growth EVER of Aspergillus and Penicillium molds under the hull of my tank. In addition, drying clay will shrink, and if you have a tank mounted, the shrinkage can make your tank tracks look really funky. If they were parallel and even before, they won't be later...
8. You can also add any ground cover to your clay at this time--while still wet. For an example, look in the Armor forum under the heading "Marder Pics." I added several different shades of ground cover to my Marder base. If you decide not to add ground cover, you can add addtional paint and drybrush when dry, or you can leave it the original color that you got from adding the Liquitex acrylics at the beginning--it's up to you.
Hope this helps you a little bit.
Gip Winecoff
Hope this helps a little