A couple of years ago I was really rubbish at painting until I realised it's all about knowing "how" to paint, with that I mean method not skill.
I recon most beginners want to make their miniatures look clean (smooth colours without any overlapping layers of paint). Due to the fact that I don't have any natural painting talent I've been trying to perfect different methods to achieve this kind of result, clean but not golden daemon standard.
The following is a couple of pointers for beginners or soon to be painting fanatics out there
* Patience: Painting is supposed to be fun and relaxing, if you are stressed or have something other than, say, Empire on your mind, do not paint until you can give the hobby your undivided attention. This will also help you get better painting results, trust me on this!
* Start of with the colour that will cover most of the miniature (or more than any other colour) and stick to it until it's finished. If you make mistakes don't worry. My models usually look like crap until the final touches, that's when I clean up my mistakes.
As a side note, go to your local GW store and check out the book called "how to paint citadel miniatures" and turn to page 77. As you can see the painter makes loads of mistakes by overlapping his brushstrokes over detail but cleans it up in the end. His models still look awesome.
* A clean basecoat: Make sure you start of with a good basecoat. If you're painting grey over black primer, paint a codex grey coat until you cover the black primer COMPLETELY. I can't emphasise this enough, the base coat determins how good and clean the end results will look. A common mistake is painting faces and skin colour by starting with a sloppy base coat thus getting very dirty and unatural looking faces.
* Use water: Always thin out your paint with water (drybrushing is an exeption). Make several thin brush strokes instead of 1 or 2 "thick" ones. This will help you achieve a smoother layer.
With these guidelines in mind you can't really go wrong. The only real way of getting better, though, is practice (I know it's boring to hear but that is the sad truth unfortunately). But first and foremost remember that your painting reflects the mood you're in while painting. So make sure you're having fun!
Feel free to post additional tips and tricks