About priming: pick your primer: other than a certain primer color being the majority of the color scheme there are reasons for picking your primer: black is obviously good for dark colors and speedpainting (you don't really see if one misses a spot with a black primer), with a grey primer you get more natural-looking tones and finally a white primer makes painting bright colors easy and lends itself for some speedpainting techniques such as heavily washing the model with a color to create more vibrant and fast results compared to black. As far as I'm concerned white primer produces the best results.
If you'd want to get an instructional dvd I recommend the Hot Lead DVD, it's one of the best instructional painting DVD sets out there, if you're ready to burn some 40-50$ on it, but it it by no means required. You can pretty much grab the same info from around the web either from step by step tutorials or from youtube videos.
Paint-wise I'd say go with dropper bottles for easier mixing (don't be afraid to mix your paints!) and avoiding the paint drying in a pot. This means either Vallejo (Either Game- or Model Color), Reaper Master Series or the new Army Painter stuff. I would currently shy away from the Army Painter range because of how small it is. So Vallejo or Reaper, it comes down to preference (read reviews; one isn't superior to the other the paints are just different). That said, everyone needs a pot of P3 Morrow White, that stuff is amazing (and PP does have some neat colors you might want to get). Picking up the GW Badab Black, Ogryn Flesh and Devlan Mud washes and some of their metallics wouldn't be a bad decision either.
Thinning your paints with water goes a long way but if you want some additional tricks up your sleeve, get some drying retarder, matte medium and flow improver. Drying retarder allows you to extend the time you can work with the paint before it sets making it ideal for stuff like blending or feathering. You can thin your paint with matte medium and water for glazing - matte medium allows transparency without turning the whole thing into a wash. Finally flow improver (or flow-aid) breaks the surface tension of the paint allowing it to flow into recesses making it ideal for washes and such; granted you can substitute flow improver for dishwashing liquid but I wouldn't want to risk the bubbles and soapyness.
As far as brushes go, natural hair IS the way to go. Just remember to take care of your expensive "main" brush. Natural hair holds a point really well so you don't really need supersmall brushes as you can do the detailwork with just the tip of the brush. I'd also grab some lower quality brushes, a size or two bigger for basecoating a flat one for drybrushing and a synthetic brush for mixing your paints on the palette.
If you're using dropper bottles you'll want a palette (and even if you decide not to, you don't paint out of the damn pot; YOU DON'T!!). I'm currently using the back of my eGaspy blister but a real palette, especially one with wells isn't a bad investment, just make sure it's something that's easy to clean such as porcelain. An alternative type is the wet palette. PP has a fairly cheap one you can buy but you can make your own, you just need a container, a wet sponge and a piece of baking paper; the paint absorbs water through the paper keeping it wet for long periods of time.
Now onto painting.
Here's a color wheel.
And here's a color wheel application. The latter can help you pick color schemes, the former is for general reference. You might want to pick up a physical one, too (
Here's a good one).
Now while I'm not an expert on color theory I can say the following: contrast is important. You can have light/dark and hot/cold contrasts in addition to those demonstrated on the color wheel. Selecting a contrasting color scheme makes your army more appealing to look at; warm colors are another thing that can make your army more appealing as opposed to cold colors. Also limiting your color palette is a good way to create good-looking models (provided the colors work together), for example you might to only want to use orange and blue in addition to black and white. Color theory can help you in general painting, too. When you're creating the 3d-effect with shade/midtone/highlight you could, for example, mix a hint of a contrasting color to the shade to make highlights "pop" more.
Something you should get is a notebook where you record your paint mix ratios and your favorite medium mixes and such. This is why I like dropper bottles; good luck trying to match a color by picking paint from the pot with a brush. With dropper bottles I can measure everything in drops. It's also a good idea to apply a bit of each paint you own to a piece of paper because the colors are a bit different when they're dry. You could go as far as to create a grid with one of each color on the x and y axes and paint 1:1 ratios of each of the colors onto the grid. You can find some neat colors and "expand" your color selection without spending a dollar this way.
Ignoring everything else for a moment, the cardinal rules of painting (at least to me) are 1. thin your paints and 2. let your paint coats dry properly. Ignoring either of the previous creates blotchy and uneven coats of paint and you don't want those.
Before you're going to do anything on a said surface, make sure it's properly basecoated after priming. This means it has to have a smooth, even surface of the paint you want. Properly basecoating a figure is probably the most time-consuming step as you want to do it with thin coats to avoid building up too much paint and ensuring a good finish. Depending on the manufacturer (and even the color) you'll probably want between 20-50% water for your basecoats (although some people add even more water). The best advice I can give is to experiment with the paints you have and settle with something you're happy with. A model with only basecoats is better than a model which is shaded and highlighted but has black primer visible under the whites.
Now if you went with the black, or even the grey primer you can have a hard time creating bright basecoats over them. This is why I love the P3 Menoth White. I first basecoat over the black/grey primer with the Menoth White and re-basecoat it with the bright color of choice.
What color do you want to use for basecoating then? Both Reaper and Privateer Press release their paints in triads (not sure if Vallejo does this, I don't think so), meaning you get a set of 3 paints: a shade, a midtone and a highlight (The shade and the highlight being darker and lighter versions of the midtone, respectively). Whichever with you should use is a matter of preference, but generally if you have a black primer you would start with the shade as it's easier to cover the black with the darkest color, then work the lighter shades on top of that. However I like to use the midtones in the triads as my basecoat as I find it helps me put the shades and highlights where they need to be as opposed to working from the lightest to the darkest (or vice versa) and finding that the midtone isn't where I want it to be, screwing up the last shade as well.
Regarding techniques
Washing: Used to create shading. Pick a color (or an ink) that's darker than your basecoat, thin it down to almost a waterlike consistency and apply it liberally over the entire basecoat. The wash will flow into recesses and create natural shading. And let it dry, damn it. If you go poking around the wash while it's drying or don't apply it onto the entire area you're going to end up with lines around the edges. You can avoid this, though, by feathering the edge. If you like more control over the wash, you can apply it directly into the recesses.
Dipping: Used to create shading, popularized by Army Painter. After you've basecoated the entire model you literally dip the model in the dip, shake the excess off and let it dry for about 24 hours. Creates strong shading and usually good tabletop level results.
Drybrushing: Used to create highlighting. Using a fairly large brush, pick a color and wipe most of it off onto a piece of paper, then brush over the model. The higher points will catch the paint creating a quick highlight effect, though the result is chalky and works only on textured surfaces. It's great for stuff like fur and hair, though. And remember: you aren't scrubbing the deck of a ship - you can drybrush with gentle, light strokes and not wreck your brush in the process.
Edge-highlighting: Used to create stark highlights and abusing the edges of the model. Using a relatively thick paint, draw the brush along an edge, preferably using the side of the brush if you can. Creates stark (at least you should be using a fair bit lighter color) and clean highlights.
Layering: Used for shading and highlighting. This is probably the most basic technique after the former. You take either the shade or the highlight and apply it onto the basecoat. You can create smoother transitions by creating color mixes of the respective colors or applying more transparent layers. If using multiple thin coats make sure the layer you're applying covers less than the previous one.
Blending (I'm referring to wet-blending, though actually means the smooth transition of colors): Applying two spots of wet color onto the model and mixing them there to create a smooth transition by pulling the paint around with a damp brush (dampening the brush with spit is great, water works if you're phobic about brushlicking). This is where drying retarder comes in handy as acrylics tend to dry rather quickly.
Feathering: A mix of wet-blending and layering. You apply a paint mixed with drying retarder onto a dry surface and draw the damp brush across the edge smoothing the transition. This is probably the best out of the three in time-consumed vs. results.
Glazing: Used to tint the underlying color, fix flaws in color transitions or to create object-source lighting. As mentioned previously you mix paint, matte medium and water to create a glaze, which has very little pigment in it, and apply it onto the area. You can purchase glaze mediums which, as far as I understand, are just premixed water and matte medium.
Lining (or blacklining): Used to create a clear separation between two areas or to create the darkest shade. Using either ink or thinned paint you draw a line between two parts of the model. Helps define shape.
Once you're happy with your model the final step before protective coating is to perform clean-up. Make sure that every color is where it should be and fix any mistakes you might have done.
