You need to know the pattern, and practice the pattern. While the judge will help at the BH level, they do expect you to know it. If you do forget something, it's not the end of the world. Just ask. But do everything you can do to prepare ahead of time to make sure you don't forget. Trialing can be stressful enough without disturbing the rhythm of yourself and your dog by getting flustered or having to stop and ask. It can be difficult, especially for those who haven't done it, to read the rules or see a diagram and translate that into what exactly to do on the field. So the best thing is to get an experienced person to walk the pattern with you and coach you on it to make sure you are doing it right, and then practice it a LOT.
I always tell new folks getting ready for their first trial to go out and walk the pattern over and over again (without the dog) so it becomes second nature. People get nervous on trial day and that can cause brain farts. The more you've drilled yourself on the pattern and have it completely memorized, the less you're likely to forget something and the less you have to concentrate on the pattern itself allowing you to focus more on your handling and your dog and less on trying to remember what comes up next.