Dear Hairsalon stylists, how should I approach my haircutting experience?

I'm a male, with mid-long length hair. My hair covers my ears, my bangs are past eye length, and so on and so forth. The gist is, I want to style my hair, and I have a certain image I want to approach. How should I approach you guys [Stylist/Haircutter] when it's time for my appointment? Some of the questions include,

• Should I tell them what I want with my hair?
• Should I go so far as to tell them I want this part of my hair cut, this part thinned, this part cut, and this part cut?
• What happens if the stylist says that I'd look horrendous? Talks in a loud voice as to say that I shouldn't ever tell my friends who cut my hair, because he takes pride in his/her work?
• What if the stylist logically states that because my hair grows in x direction, I won't get the desired effect of a flattened hair style but it'll poof or stick out?