Do not do ANYTHING you don't want the students to copy.....I can promise you they will.
I like to attend every class that the students are at, including the academics. While as a DM/DMC you really don't have to, you can start to get a feel for how the students are going to be, who to watch and who you can be a little less cautious with and you start building a rapport with them. This will go a long way when you are helping a student that has issues. There are times when whether they trust you or not will be what determines if the student succeeds or quits, building that trust early goes a long way. For whatever reason, students will often pull you off to the side with a problem that they will not take to the instructor. How you handle it depends on the problem and the instructor but at least they feel secure enough to ask you rather than not asking at all.
At the end of each day, take a little time to discuss with the instructor what went good, what not so good , what they want you to do that you didn't and what you did that they prefer you did not do.
Spend some time learning the instructor(s) as well. We have a large staff at our LSD with 15-20 instructors and every one of them is different. Some want me to demo skills, others want to do it all themselves, some prefer to handle student issues while others hand them off to me. Don't assume that one instructor will be the same as the next. Don't let your style or beliefs get in the way. If you think BP/wings are the greatest thing since sliced bread but the instructor wants you in a jacket BC, shut up and do it. It is his/her class not yours.
Be the best example of proper trim and swimming techniques you can, you are the first diver they see and it's up to you to show them what a good diver looks like......and judging from a lot of the divers I see, there are a lot of poor DMs around.
Good luck and enjoy the experience.