You can say things like “No, I don’t want that at this moment, but I would enjoy this x,y,z.” Or say “no thank you,” (picture a scenario where they’re trying to go down on you and you aren’t in the mood) and move their head elsewhere. You could also use some variations “Will you touch me here instead?” Redirect their attention after the ‘no’ by guiding their hand to the butt, breasts, or other erogenous zones.