Bring a couple of sets of dogi to the seminar. If there are multiple sessions in one day, you'll be much more comfortable in later sessions if you have a fresh, dry set of dogi to wear. Even before you step on the mat, make sure you hydrate yourself and have something in your stomach. When this happens, I make an effort to watch what the instructor is doing and try what they are demonstrating. The differences in approach are oftentimes more important than their similarities.
Seminars are often crowded - sometimes far more crowded than regular classes.
Look around you as you train and practice safely. If there are too many people, you may wish to just move your partner to the point of breaking balance. Although it is tempting to work with folks with whom you are acquainted, training with new people whom you've never met is an important part of attending seminars. Feel their approach of interpreting what the teacher is demonstrating. Once again, you can learn from the differences.