I always ask, but you're right Eric; many do not dare. That said...
X2 on the shadows. And highlights.
Both are needed to impart a sense of shape. I would also lock in the light direction. I see so many flats that are painted with the actual light direction being kinda, sorta 'somewhere above' often to the point where it's so ambiguous, the flat looks
flat. Only the girl in top hat seems to have it defined based on the light flare on the top hat, but it's not consistent over the entire figure. The rest of the pieces are falling into that area of ambiguity.
Additionally, all of the skin tones seem to be the same, or so close as to be virtually indistinguishable. The cowboy and biker(s) are
outdoor types, so their skin tones would be darker and have more contrast than the two girl busts. The girls' skin tones would be lighter and softer, but still have enough contrast to bring out the three dimensionality of real people. Girls' hair also tends to have lighter highlights versus male hair. Both girls' hair is a bit monochromatic - the blonde in the top hat especially so.
The bike handlebar - assuming it's chrome - should have more reflectivity; sky above, ground/pavement below. Ditto for the bike frame (assuming it's glossy paint vs satin or rat rod matte). The curvy bits on the handlebars are, I assume, brake and throttle cables. Should these be the same color as the bars? Should they be that thick? Don't be afraid to make minor corrections to a piece if something is over/under scale, skewed, or mishappen. Generally speaking, no amount of paint is going to fix those things. The lines painted on the headlight give the impression that the light is pointing up into the air. The black voids on the bike frame should be the same color as the background so it gives a better impression of a bike's open framework. Likewise for the spaces between the spokes (which technically wouldn't be visible on a moving bike...).
The horse is better painted than the cowboy (and I speak as one who hasn't painted a horse since the mid-70s, but is about to take the plunge). Also, the cowboy seems to be standing on top of the dust cloud (that is a possible engraving issue, which the painter can do little about). I think the dust clouds would be better represented if they were transparent, thus allowing the background to show through.
OK, full disclosure Dave: I've only painted about 15 flats over the past few years. The above is what I have learned over the course of that time. It will help if you focus on one piece at a time, plan out the painting via notes, and consult the notes regularly so you stay on track.
Good luck with it!
Slainte,
Glen
