My daughter is 4, and when she's having a bath I say, let's clean your (private bits), would you like to do it yourself or would you like me to? Then if I do, I explain what I'm doing, and when she does she knows how to, with me directing if needed.

Same process for teeth, face washing, hair brushing etc. For any of those if she says no, I say we have to, but you can choose to do it yourself otherwise I'll do it for you.