Haircuts can either be the best things ever, or the worst experiences. I personally really enjoy getting my haircut, and I seem to have somewhat mastered the art of getting the "perfect" haircut!
Do your research.
There are websites that can help determine your face shape, and can then determine what hair cuts will look good on you. Just remember that just because the haircut looks good on someone else, doesn't mean that it will look good on you.
Instead of attempting to describe exactly what you want (let's be honest- this never goes well), find a picture similar to the look you're going for. Try to find both a front and back view of the haircut so that the stylist knows exactly what you want. When looking for haircut inspiration, my go-to is Pinterest.
Ask them their opinion.
If you are unsure about a color or length that you are considering going for, don't be afraid to ask the stylist if you will look good with "XYZ" style of hair. They will either say yes or suggest a slightly different color or cut.
If your stylist asks you if you want something longer or shorter or if it's fine the way it is, speak up and tell the truth! Sometimes I find myself saying that "it's okay" just because I don't want to hurt the hair stylist's feelings, when in reality I am the one who will have to live with the hair cut. Don't be afraid to speak up!