If your partner tells you how they think you should do your line, how you should behave or dress in the scene, try saying something like, "I know you are trying to help me, and thank you, but I usually can do a better job if I work through it myself. I'll figure it out." If the problem persists, tell your instructor immediately. Being directed by your peer is not what you are paying for when you signed up for your acting class. Feel your way through this, follow your gut and you will know what to do.