The Basics: No matter how well a kit is put together without paint a model is only half finished. Advanced modelers paint everything, even if a part is molded in the correct color. It is easy to discern raw plastic from a painted surface. Beginners can greatly improve the look of an aircraft model with just two cans of spray paint: a can of gray or blue for the bottom and a can of green for the top. Many WW2 U.S tanks had a coat of olive drab applied to the whole vehicle before leaving the factory. This meant the treads, tools and everything else was painted--easy to duplicate on a scale replica. The best thing to do is jump right in.Easy to do Tank Treads: Old rusty tank treads can easily be duplicated with an inexpensive can of Automotive Primer . To make them more realistic apply a dark rust (red mixed with black) wash . When dry drybrush gunmetal or steel on the raised surfaces which contact the ground.
Intermediate: Wash: A coat of watered down paint, usually a dark color, that brings out recessed panel lines, engine grills, flight control seams, landing gear and suspension detail, and
any other cracks and crevices. A water based paint works best since there is no thinner to ruin the paint underneath. Apply with a thick brush and sop up the excess with a dry brush or paper towel. Washes adhere best to matte or satin finishes, since a gloss surface will cause the paint to bead and run off. Washes can be applied to a gloss finish, but the paint may have to be worked into the crevases and the excess sopped up with a towel or cotton swab.
A wash is also good to simulate oil stains on vehicles, sweat stains on figures and, when applied with the direction of airflow over an aircraft it resembles the dirt and wear accumulated through flight.
Applying: To cover a small piece or subassembly apply the wash, sop up the excess and allow to dry in the position it will be when installed on the kit, and let it dry for at least a day before continuing. To cover a whole subject, such as a complete fuselage or tank chassis, apply the wash to one side, sop up the excess and place the assembly 'washed side' up allowing it to dry before starting on the next surface.Wash examples: airflow streaks, recessed panel lines, crevices Dry Brushing: Just the opposite of a Wash, dry brushing uses a light color to bring out the highlights of raised panel lines, nuts and bolts, wear and tear, and any other protruding features. Since the paint goes on 'dry' any type of paint should work. A bit more difficult than 'washing' it takes practice to master.
Applying: Use a brush 'A' (any brush) to place a dab of well mixed paint on whatever you use for a palette. Use brush 'B' (a perfectly dry, wide, soft bristled brush) for the area to be painted, and dab the tips of the bristles in the 'puddle' of paint. Take a few brush strokes on a piece of paper to even the paint on the brush and repeat until the paint barely appears on the paper. Now lightly paint the surface as if you were dusting the model and apply just enough to highlight the raised portions. When brush 'B' gets too saturated and begins to leave streaks then it is time to clean it and let it dry before continuing or switch to another dry 'B' brush. 'Less is More' or 'When you think a dry brushing job looks just right then it is probably too much', i.e. when your ten year old looks at your finished HMMV and asks "Is that supposed to be snow?", you've over done it.
For real life examples of what dry brushing is supposed to resemble visit your nearest National Guard armory or a junkyard. If they are too far away or out of the question, look around your neighborhood for a weathered, old fire hydrant. I've seen a few where the paint is oxidized and fading on the bumps and bolts, but bright in the shaded areas and grooves.
Dry Brush examples: nuts, bolts, panel lines Wood Grain: Making plastic look like natural wood can be a challenge.
For solid wood paint the whole piece a light tan. When dry use a fine point brush and paint alternating dark brown, black, white, and light brown lines of different widths and in a wavy pattern. Be sure to include a few knot holes. When all this is dry apply a dark brown wash.To simulate multi-sectional wood: Paint the piece a solid color. Let dry. Cut strips of low-tack tape and place where the wood sections would be. Paint the unmasked areas with a different color. Create the wood grain with the method above. Advanced: Metallic finishes: The most I have done is simulated bare metal under chipped paint and basic components such as landing gear struts and gun barrels. Wayne Stacy ( awastacy@hotmail.com ) sent me these photos of his P-51 painted with Alclad II paints. Weathering: Creating rust, dirt, mud, oil, scratches, exhaust and muzzle blast residue add realism and are the last step to 'authenticating' a kit. Goto: Weathering for more details. 
Airbrushing: Another large subject. Goto: Airbrushing for more details.
