Are you going to get your hair styled before an event? We have two words for you: bring pictures. It can be difficult to adequately describe a hairstyle, and if you don't have the words, it's easy to get flustered, unsure, and unassertive. Prevent that from happening by doing some research and providing a stylist with pictures. It will give them a reference point for how you expect your hair to look at the end of the appointment.
If you have provided pictures and the stylist still isn't going in a direction that you're thrilled about, say something along the lines of: "hmm, I was hoping to have more volume," or "I would like it to look looser, natural, and effortless." It's not rude, it's actually helpful to the hairstylist, who wants you to love your hair.