two methods. Sorry if i repeat something you already know.
For 10-20 minis at a time:
Spraypaint black from everywhere
Spraypaint white, but only from above (don't do pffffffffffft. Never. Do pft pft pft pft. Takes one minute more per model, but is less risky and has better results!)
The result should look
like that.
Paint the mini in base colors, use bright tones; a little bit thinner than normal. They will automatically be a little bit dimmer where the primed model stayed black.
For the right color thickness, i can advertise strongly to use a
wet palette. Without it's difficult to get it right. On a wet palette, with a single twist of your pen, you can adjust the amount of color, the perfect pen tip and the thickness of the color. Not to mention you can mix as you want but that's not for fast-painting.
Care for the player's perspective, not so much for the rest.
That means, paint hands, weapon, face, upper side of the chest, shoulders and upper side of the arse carefully.
The underside of the belly, the armpits, underside of anything, the shoes and all the other invisible parts: no need for careful painting.
dip what you did in a tin can of
Army Painter. Quickshade in a Sepia-like tone works for most of the color schemes. Don't forget to shake the can before opening it. If you shake it, the shade will be stronger, if you don't the shade will be more transparent. Use a tool, pliers for example, to dip the mini.
Afterwards, shake the mini so that what's too much comes off. Let it dry standing, so that the shade flows to the lower parts of the model.
when it's dry, shake up a can of matte transparent protection spray and do the pft pft pft thing again.
Shaking it up is important because most of the matte spray products have the problem that the small crystals for the matte impression settle down at the bottom end, and the rest of the fluid is high-gloss. So better shake it an extra minute, until the arm hurts. Be VERY careful with matte spraypaint: It can become grey where too much of it settles. So really think about the pft pft pft thing.
The more expensive method:
Spraypaint the miniature with an airbrush before assembling, each part with two or three colors, but do 30 minis at a time. The little bucket on the Airbrush has enough volume for that.
Then glue it together.
Do some details with the pen. (only where necessary).
Problems with the second method:
* You need an airbrush.
* You need airbrush colors.
* You need models that needs assembling. (So they're new & they are made from plastic)
So it is expensive. The typical ebay-hunter among us won't have too much use for the second method.