I typically just ask, i try to give them the option of 3 objects, ideas, colors. 3 anything to atleast give me a base of what they want. but i mean if they are asking for art they probably like your style already so maybe stick with the norm
GUKU/ donnie - those are looking super good, donnie that is intense man lots of things going on in that, the top where its getting all busy looks super good with the clean simple bottom shapes
guku - lovin the yellows and greens, that one blue arrow on the top needs a detail line or something? but damn those colors and lines are poppin off that wood panel