We adopted 6 years ago, and once everything was settled I went along to a few courses as an 'adopter trainer'.
The days can be very intensive and at times emotional. They really get you thinking and can be used as a springboard for discussions during homestudy.
Try not to have any commitments in the evenings and make sure you have some easy-to-cook food in the house.
If you have relevant experience then it is nice to share it with the group.
You don't need to share anything with the group that you aren't happy to, and you should be allowed to leave the room to compose yourself if any section is a bit emotional for you.
Make sure you have your phone off and work know you really are uncontactable. Try not to get sucked into taking work calls in breaks etc it gives a bad impression (especially if you are late back!)
Wear clothes you are comfortable in.
You don't need to do lots of questions / speaking etc, but if you stay really quiet you run the risk of looking disengaged.
Try not to be confrontational. If you disagree with something ask for clarification / saying you don't understand why etc. Don't say they are idiots!
The SWs will be taking note of you. They aren't looking for a specific profile, but they may well be thinking already about what type of child might suit you.
Be yourself.