@Kiblams: Yeah, they must have taken my idea!
I should probably find that line and finish it sometime..
@Elliott: A lot of the results comes with time and experience. That being said, knowing proper techniques can be very helpful to get better results in less time.
Citadel is fine when starting out as it has good coverage and is a bit faster since you can take from the pot. Vallejo comes in dropper bottles, so you need to work from a palette, but can get exact color matches and wont ruin your brushed from accidentally dipping it too deep into a paint. Also they don't dry out like Citadel tends to do, which is a big plus in my book. At the time I used citadel colors for this army.
My Army colors:
Airbrushed Mechrite Red
highlights in an orange/red mix
Cloth and terrain:
Iyanden Dark Sun
highlighted with bleached bone
Machurius solar orange
I used it watered down to fill in the weapon lines.
Bleached Bone watered down 1 or 2 layers
White watered down layers. I recommend the Vallejo Model Air White. it is meant for airbrushes so it is pre-thinned, so you can apply it quickly without getting that chalky effect that can happen with whites.
I do use an airbrush for my vehicles and also for priming and base coating all of my units. I have not used it much for shading on infantry or suits. Starting from a color instead of black or white primer can be a great boon, and is something I like to do for my friends to motivate them to paint their army.
I learned on a cheap $50 Aztec airbrush, and eventually upgraded to a Badger Renegade Velocity and a compressor. It has a learning curve, mostly around the mixing of paint to the proper level, and cleaning.
The camo stripes are freehand, built up over a few coats. I tend to go back and forth with red and black, until I have smoothed out my edge. I also use a brighter red to do this so I don't have to match the specific gradient of red. You could easily replicate this with painters tape as a masking, but I wanted mine to be on a curve. If you use painters tape, don't water down your paints, or airbrush for best results. Watered down paint will seep into the tape and make a mess of the straight line.
In terms of crisp paint, taking your time with watered down layers will bring out colors and give you the ability to fix mistakes as you layer. The downside is the more layers you add, the longer it takes. On a lot of this army I did not do much layering, but I did keep my paints thinned. I use about 50/50 paint to water.
Every time I pick up some more paint I always use the brush on some scrap or my thumbnail before I apply it to the mini. Especially when you have watered down paint, applying too much can flood the whole thing. You want to be applying just the right amount.
You should ideally have a few brushes, each for a different use. A flat brush for drybrushing, round brushes, a detail brush if you want, a brush for taking paint out of a paint pot.
90% of my painting is with a Round 0 or 00 brush. I even do most of my detail with it. I find that smaller is not necessarily better, it is all about how well it keeps a point and how much paint it can hold in the middle. This is effected by brush quality and also how well you treat the brush.
In terms of quality, I use Kolinsky Sable brushes and will never go back to the craft store aisle brands. I did use(and abuse) cheaper brushes for a very long time. Starting out they can be fine, just make sure to check the brush with the cap off to make sure the point looks acceptable.
Cheap brushes can last if you take care of them, and expensive brushes can die just as quick if you don't.
Keep paint from drying on the brush by regularly washing it every hour or so.
Do not let paint get up where the bristles meet the metal (ferrule). Dried paint there will cause your brush to splay out and be useless for detail.
Getting a brush cleaner soap can also revitalize older brushes. I use The Master's Brush Cleaner and Preserver and it works wonders.
A wet palette can be as simple as a plate with some soaked napkins and a piece of wax paper on top. The idea is you can put paint out onto the wax paper, and it will be kept from drying by the water below. This means you can work longer from a mixed paint, and also provides a good place to thin your paints. Some real palettes can be sealed and keep the paint good a few days, but I have not had much luck with commercial palettes. My best palette ever was a Flames of War plastic plastic blister package along with the foam that came in it as the palette sponge.
Light! I almost forgot light, but it is very important to be painting in good light! I bought two OTT lite desk lamps with natural daylight bulbs, and they go wherever I go to paint.
Hope some of this helps, and let me know if you have any other questions!