You may not be a great painter. You may not be a great modeler. But by god, you can base a model. I promise you, a mediocre paintjob can be elevated by a great base and a great base job can reach levels of the sublime by a good base.
Let’s look at it. A model’s base makes up a solid half of the visible surface area of the model, most of the time. First of all, you should work on the base as part of the miniature’s assembly. That way when you’re priming the model you’re also priming the base and you don’t have to go back and do it later. So just finishing the base with some dirt, painting over it, then dry-brushing that and adding some patches of static grass will give you a pretty great base. Take a look at this.
That’s basically all this guy is. Just some dirt that got painted grey, then drybrushed with a lighter grey. Add a few patches of static grass and *poof*. Insta-cool base. But do you want to take it a step further? Of course you do. Enter: cork bark.
Cork bark is available from terrarium stores, but you want to go to eBay because it’s cheaper and of course you want it cheaper. Get the bark, not the cork that they use for cork boards. The bark looks like rock. The board looks like chopped up concrete. The rock can achieve such effects as these:
It’s also really easy to work because, well, it’s cork.
Another tool in your base-building arsenal should be pumice paste. Vallejo makes this stuff mostly and it comes in these 6.75 oz jars and in a wide variety of granularities, but you’re pretty much good with the standard grey or white. The grey is the most coarse and the white is medium. The sand one is great if you’re doing a desert themed army because it makes great dunes. The jist of this stuff is that it’s a somewhat sticky paste that you can spread on with an old crappy paintbrush (use a kind of larger one, like a 1/4 inch or larger and NOT one you care about) and it will create uniform, gritty dirt on your base that’s easily shape-able and can fill whatever spaces you need. A lot easier than doing the glue and dirt from your back yard, and much better results.
When you really want to take it to that top-notch level you can start adding other models to your bases, sculpting special scenes on it, or even including entire pieces of terrain on them. I won my third Golden Demon entirely because of the base of the model (I used a whole tree from the Citadel Woods kit to put a Forest Goblin lord on a Giant Spider in).
As I said earlier, bases are an easy way to take your painting and modeling to a higher level. Simple, sure, but it will gain you a lot of points in a tournament and tie your army together in a way that very few other things can.