Hi Marcin.
I've never really thought about my approach to clothing, except that I have always been concerned with getting the lighting right - usually the light coming from the front and above. Here, I used Vallejo Grey Green as the base colour for the overalls, and modulated the shades by adding touches of Camo Black Brown, English Uniform and Off White. The lighter tones and softer shadows are at the top, then they fall off towards the bottom where there are sharper contrasts. Lighter colour schemes such as this one tend to need more subtler shading, which is very hard to get right.
I started painting each area by covering it with a mid tone, ie intermediate shadow, a mix of the Grey Green, English Uniform and Black Brown. While the area was still wet, I started building up the highlights with pure Grey Green, the wetness enabling the blending of the shadows with the highlights. The highlights were then built up by adding increasing amounts of Off White to the Grey Green. Where necessary, the shadows were darkened by adding more Black Brown and English Uniform to the base colour. It's essentially about trying to work wet, and that means working on small areas at a time - left front of chest, right front of chest, front of left arm and so on. I tend not to thin the paint too much to avid streakiness.
I hope this makes sense.