You've booked yourself your first gig. You're sitting on the modeling podium in your robe, waiting for the session to begin. What next?
The Art of Holding Very Still
Drawing groups are generally structured to start with shorter gesture poses (generally between 30 seconds and two minutes), and work up to longer poses (generally between 20 and 40 minutes). Along the way, you can generally expect breaks every 30 to 60 minutes.
Gesture poses are the chance to get dynamic. You can select poses that you wouldn't be able to hold for extended periods of time, but can hold for a few minutes. Putting yourself off-balance, leaving limbs unsupported in space, stretching, and unusual weight distribution are all ideas to play with for gesture poses. So long as you're capable of holding the pose for the given window of time, consider it fair game. More on gesture poses can be found here.
As the length of the poses increases, begin opting for poses that will be easier to maintain over time. With longer poses, if you settle into it and suspect that any body part will start hurting, know this: it will. It will hurt more spectacularly, and more vibrantly, than you can possibly imagine until you've decided to test that theory once.. twice.. or a dozen times, if you're a slow learner, like me.
Pain aside, it's easy to start drifting out of longer poses. Twists can be difficult to maintain, and limbs that aren't supported will often begin to drift. I try to keep all of my extremities in contact with either my body, the floor, a stool, or something else that won't be moving. That way, I have multiple points of reference as to how I was posed. To keep my head in position, I let my gaze fall directly in front of me, and then I pick a visual point to focus on.
Over the course of the session, remember to rotate. This is especially true if the group barely fits in the space, and people can't move easily if they want to draw from a different angle. It can be frustrating for artists to get a disappointing angle for every single pose through the evening, but not being able to easily move. Try to give everybody at least a few front, back, and profile views along the way. Similarly, vary between sitting, reclining, and standing poses.
From time to time, you'll encounter "long pose" drawing sessions, in which you're holding the same pose for the entire session. When working with painters, you can also expect to hold one pose through the entire session. Of course, you'll still get breaks during long pose sessions. Before the first break, the organizer may put tape down on the chair to mark where different body parts were.
After the Gig
I generally leave life modeling sessions feeling very tired, and very hungry. And satisfied. Beyond taking care of your food, water, rest, and stretching needs, there isn't too much more for me to suggest.
Though there is no substitute for experience, I hope that this guide can help novice life models on their way. My inbox is always open for specific questions as well. Happy sitting!