Do you have an irrational fear of painting miniatures, because you just know you'll mess it up? I had the same problem, and still do every time I sit down with a freshly primed miniature. Unpainted, the miniature is basically perfect. It's just really really plain. But perfect. And when you start painting it, there's inevitably going to be a mistake made. A careless brush stroke here, a drop of paint that gets away from you there. Something's going to go wrong, and it'll ruin your miniature forever. Except it's not forever. Painting mistakes are really easy to fix, and keeping that in mind can help you take that terrifying first step toward having a painted miniature.
These are the tyical steps to preparing a miniature:
I find the second step the hardest, to be honest.
The first step, assembling the model, isn't always easy, but it's fun. It's physically like a puzzle, or like LEGO, because you're taking physical parts and putting them together. It's great.
The third step is hard, too, but it's also fun. But it's terrifying. That's why we're here.
The second step requires thought and precision. You have to decide what colour of undercoat to use, and you have to know how spray a light coat for maximum coverage. You can over-prime. I've seen it done. You can under-prime. I've done that, myself.
Sometimes it makes sense to undercoat with white or light grep, especially when you're painting with high contrast paints. Othertimes it makes sense to undercoat with some other colour, usually the predominant colour of the model (red for Blood Angels, blue for Ultramorines, black for chaos marines, and so on).
Whatever you choose, though, your undercoat becomes your canvas. Anytime you make a mistake, in the worst case scenario, you can let the mistake dry and then paint over it in the same paint as your undercoat, and you've got a clean canvas.
For my undercoat, I use Citadel White Scar a lot, because I like the way Citadel Contrast and Vallejo Xpress Color paints look over top of it. When I make a horrible mistake, here's how I deal with it:
It's that easy, every time.
You don't always have to start all the way back at the beginning, of course. Maybe you've got a base coat of White Scar (or whatever), but you've layered red over it, and then you get some gold in a spot where it shouldn't be. You can probably just let the gold dry, and then paint over it with red.
Citadel Contrast and Vallejo Xpress Color are, to varying degrees depending on the shade, not opaque. That's how they achieve their automatic highlighting and shading effect. Painting over a mistake with a high contrast paint doesn't always work, so going back to your undercoat sometimes is the most practical way to correct an error.
Mistakes happen, and because miniatures cost money to acquire and time to paint, mistakes can feel especially egregious when you're assembling and painting them. It's easy to fix your painting mistakes, though, so don't let the fear of making a mistake keep you from completing your models. Get them painted, and use them in your games.
T'au soldiers photo by Seth Kenlon. Creative Commons cc0.