3 things to do to guarantee you don't get a bad haircut!
1 - Don't style your hair the day of your appointment. That way your stylist will be able to see the natural texture of your hair. Talk to your pro about how much time you're willing to spend styling your hair and which products you'll need to get the look at home.
2 - Bring photos - Of both what you like and what you don't. You might describe something you want, but to your stylist, it means something different. A photo makes it easy to know exactly what you mean.
3 - Ask the stylist to show you exactly what she plans to do. They should be able to give you an idea of the end result by holding your hair at different lengths.