Well, seminars are the way to go if you want to know if you like it or not so you will see by yourself.
Regarding "How to get the most of it", what is your experience in MA for the moment?
Experience? I just began training 1st week of February and I am a white belt. This is not my first time training however, I trained most as a teenager(47 now) for several years in Kempo and wrestled 3 years in high school. I guess I would classify myself as a beginner with a bit more knowledge than the typical beginner.
Usually, before a seminar, I make sure that I am physically ready by strengthening the weak points that are going to be stressed (neck and core workout for BJJ or Judo, wrists (my weakest point) stretching for Aikido, legs stretching for Tae Kwon Do...)
When it comes to CQC, it is a bit different, this is usually less exhausting but requires proper joints conditioning (similar to Aikido).
Then some rest before the seminar.
At the seminar, 2 full sets of tshirts/shorts/underwear for the seminar itself, chocolate, lots of water... Just think about what you would need if you were doing 3 normal trainings in a row.