its really hit and miss with mass shoots. sometimes u can get some friendly shooters, sometimes it can be a mass free for all.
also, there are considerable time pressures when shooting - either u will only get allocated a short time one on one... or its a free for all on one model.
as such, its not really the best time, to be trying to figure out what mode to shoot in, how to adjust your exposure, how to fix your white balance, whether to shoot RAW or JPEG etc etc.. because on top of all of this, u need to be working on composition and directing the model and paying attention to lighting etc etc etc.
what i would suggest is this. in order to get maximum use out of a paid model shoot... first be thoroughly familiar with all ur cameras functions. also, master your basic photography skills like basic composition, using different AF points, framing, and bracketing exposure. try and figoure out, when u want to shoot wide open, for bokeh, or when u want to use a higher F stop for bigger DOF.
u dont need to pay $$ to belearning this on the day.. can just stay in ur room, lie on ur bed with the manual, and shoot and learn to your hearts content.
also. do ur homework. go and look at the portaits that get posted here and on other sites. look for the comments that get made etc etc... www.photosig.com is anther good site with good C&C.
from reading all of this, u will start to get a rought idea of the general do's and dont's for portrait photog.
before anyone jumps down my throat, im not saying that one has to follow any rules... but just like the rule of thirds, its good to know the general guidelines.. before u can then decide to what extent u want to break them.
if you can do all that, then its worht going on a model shoot, because u will get more out of it... and better value for money.