at first my unskinned model. occlusion is good way to show all the geometry readable

then unwarping and pre-baking ambient occlusion grayscale map. it perfectly shows all intersections and geometry on skin. also shadowed diffuze map looks much tragic ingame.

after all preparations i coat my devastator with base colors(cast iron and steel) and some filter made scratches, after filtering i erased scratches everywhere except corners of model.

The other critical part of miniature painting(we lay with miniatures, not real tanks :) keep it in mind) is lightening of corners. take another layer and enlighten corners with blend effect
now it looks more volumetric, yeah?

next step is to draw basic texture under shadows and light areas. also i am adding some noisy dirt and others, its really "alives" miniature. think carefully jf model constutution and intersections - they must be shown

after all - scrach and age your model for best scale-read results and dramatic look
also, keep in mind spaces of housecoloring. it must be part of texture not just chaothic sripes over detail!

There was discussion in team so some geometry were added. do not mind some model changes.
Make final spellcheck(texture bugs) correct it and add another overbrigtening jn corners(invert shadowmap and make small brightness/contrast ajustments to light only corners.... also it is good to tune colors to other models in projects(so you model is not darker or brigter, precisely same style and color).

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final render after all changes and extra owerlightning