It's very important to have a hair and makeup trial in the weeks before your wedding even if you're planning on doing your own hair and makeup. The morning of your wedding is not the time to experiment.
At your trial remember to bring a digital camera, not just your camera phone, and make sure you take pictures of yourself from the front, both sides and for your hair, from behind. This way you can see what you'll look like from all angles.
Your makeup artists should take notes, writing down exactly what colors she is using on you so on the day of your wedding she is not trying to remember which shade of pink blush she wanted to use.
You can ask for a copy of the notes to have for your own records and if you want to purchase any of the products, such a the lipstick or liner, make sure you have the brand and color name correct.