See? And there's still more. There's always more...
After the glue has dried, take your entire army and prime it up. The glue will hold the sand onto the bases from the bottom, while the primer will seal the sand from the top. Also, this cuts down on your work for later.
I typically don't base my models before I prime them, and wait until the whole army is fully painted. I learned different, and it's a true disservice to my training. However, it doesn't really make a difference to the finished product. Really, this step is a safety net and cuts down on later work.
Once the bases are completely dry and solid, it's time to paint them. DO NOT ATTEMPT TO PAINT 'ALMOST DRY' BASES! It's an epic fail everytime, and usually removes the sand from the base. Save yourself the frustration and wait a couple of hours before painting the sand.
To paint the sand, simply grab your good paintbrush and pop open the shadow-color paint you've chosen. Create your puddle of paint on the tile (not near the glue) as normal, and then paint it onto the sand. If you add a little more water than normal, you'll find the paint actually 'seeps' into the sand faster. But don't add too much water as it'll 'wash' the sand instead, and that looks terrible. After basecoating the sand, set the model down and let it dry. This'll take a couple of hours again as wet sand doesn't dry quickly.
After you're SURE the shadow coat is dry (and you must be sure), it's time to add the next color. Using your good brush, simply drybrush the base-color paint you've chosen. It should be starkly brighter than the shadow coat, as the drybrush should be rather heavy. This may require you to do multiple layers of drybrush on the base to get it right, but it's worth it.
Once you've drybrushed all the models with the base-color, it's time to finish the sand. Simply use your highlight-color paint and good paintbrush to drybrush the last layer on. This layer is literally a highlight for the sand, so don't drybrush too heavily in this step. Luckily, there's no dry-time involved for both of these steps.
To finish the bases, pull out the ring-color you've chosen, grab that good paintbrush, and prepare for the hardest part of the process...
Create a puddle of the paint on your tile (away from the shadow-color and glue) and add water as normal using your good brush. It generally helps to add less water at this stage, as the paint already has a hard time sticking to the outside of the bases. Then, using your good paintbrush, basecoat the outside ring of the base (or border, if you're working on FoW). Be sure not to overpaint onto the sand or the model's feet. Even more importantly, DO NOT touch the model with paint on your fingers. I can't tell you how many beautiful models I've ruined at the last minute, just because I was sloppy in basing. Once you're done with this step, simply put the model down and marvel (and clean out your brushes one last time). It'll take almost an hour for the paint to fully dry, so that's an hour of admiring you can pile onto your doods!
You can also add static grass, flock, and other decorative things to the bases. That'll be another blog sometime in the future. For now, it's all about the basics.