I can’t write you up a Painting Minis 101 handbook in a forum post. What I can tell you is that the information is readily available elsewhere. Dakka-Dakka, for example, has a ton of tutorials in their forum. YouTube is full of fantastic video tutorials, from the barest of basics to the downright incredible. You can buy thoroughly illustrated, well-written books on the subject in pretty much any store that sells minis.
It is absolutely worth it to get some kind of handle on whatever passes for theory when it comes to painting miniatures. Because while it can be an art, it is first and foremost a craft: there’s right and wrong ways to do things, and a fair pile of hopelessly unintuitive stuff you’ll never figure out on your own, but which drastically affects what you can achieve. Really, you are waaaaaaaay better served buying a book on this than an additional box of paints.
[li]The most basic way to paint metal, is to start with black as your base colour. You want the entire area solidly, uniformly black. If we’re talking most of the mini’s surface, consider spray-painting the miniature black. It’s both cheaper and easier than airbrushing.[/li][li]Now it’s black, you need mix your silver and black paints, roughly 1 part black and 2 parts silver. Don’t thin down the paint, it’s exactly fine out of the bottle.[/li][li]You want to use a fairly large brush, and while applying almost no pressure you’ll need to stroke on your mix using the side of the brush, not the tip. Use as long strokes as you can.[/li][li]Once this is dry you switch to pure silver. A drop of paint should be enough for every mini in the pic you posted. Thin down the silver with water at about a 1:1 ratio.[/li][li]To apply this very watery silver, you’ll need a blunt brush you aren’t afraid of ruining. And some toilet paper. Dip the tip of the brush in the silver, then wipe it off on the toilet paper until the brush only leaves a faint trail of paint. Now gently brush down the miniature with the very tip of the brush, very much as if you were dusting with a feather duster.[/li][/ul]
With a bit of practise this 3-step process can look damn good. And until then you can make it look damn good by applying a very, very watered down wash of pure black (or ideally, extremely watered down black ink).
As already mentioned, one of the reasons you should test out your colour scheme on paper before you inflict it on the mini, is because it really does give you a very good idea what the end result will be like. If you’re having trouble figuring out how to make your minis stand out a little, please do try this. It’s very easy to gauge whether, for example, painting the major areas of a minis shoulder pads red, will look good, if you have a rough draft to try it on. And please believe me, it doesn’t matter how craptastic you are at drawing. Nobody but you is ever going to look at your colour tests, and they absolutely do not need to look even vaguely recognisable to anyone but you, to be insanely useful to you.
Generally speaking you should get comfortable with the idea that pretty much every part of every mini needs to be painted 3+ times in different ways, usually with different techniques. And you should get your mind wrapped around the idea that you “paint layers”. That is: you start with the darkest colours that needs to be in the deepest recesses the mini have. From there you paint on the lighter colours of the neither raised or recessed areas. And finally you paint the lightest colours on the most protruding areas.
That’s a rule of thumb, mind. You always start with the most recessed bits, because it’s very hard not to get paint all over the place when you do them. But they’re not always the darkest colours. For example, anything that’s supposed to look like a light source, reverses dark-to-light thing - typically going from a white-orange mix to a black-grey mix.
You should also not ever think of washes, inks and the like as a separate step. Or… Almost never. If you’re feeling ambitious though, you could try to shade the armour of a mini like the big sword+shield guy in your pic.
[li]Start with a uniform white base coat.[/li][li]Mix something like Sapphire Blue and white on a 2:1 ratio, and thin it down until it’s the consistency of a wash. Add 1 drop of dishwasher de-streaking fluid to the mix.[/li][li]Now use a fairly large brush to give the mini 10-15 coats, the first from the tallest point to the base and each successive wash starting slightly lower down on the mini.[/li][/ul]
The end result is you have a blue armour that looks just shiny enough to be some kind of metal, with fairly natural-looking built in hilights and shadowing. Be warned, though: as simple as this sounds, it is really damn hard to do it right. At the very least try finding a video tutorial of it before trying yourself. Oh yeah and… GW has some special wash paints that makes this approach a lot easier than regular watered down paints.