'Twas an Irishman, Bob Carlos Clarke, who gave the best advice on working with models - though some of it is scandalously incorrect! Very much 'do as I say, not as I did' stuff, but he knew what he was doing, and wrote it all down in 'Shooting Sex'. Most of the advice applies to portraiture just as well as to erotica, so it's worth reading once, at least!
Talk to the model. Draw her/him out. This is actually much harder to do at a group than on your own, though groups are less intimidating until you have confidence that you can actually do it. Once the conversation is flowing, you will get animation: when it slackens off, usually, you will get stiffness and formality creeping back in, unless the model is experienced or very relaxed with posing. Once you've built a working relationship, it all flows.
Quite a few good togs suggest talking for a while before you start to shoot - very hard indeed at a group event, though you can make a point of chatting during a break, perhaps, and holding back while the young men (and maybe the older ones, too) rush in and do obvious stuff. Should you choose to exploit it, you have a natural advantage, as a woman, in terms of credibility, and obvious freedom from ulterior motives: we men really
have to work at it, to avoid appearing crass and suggestive. Some people have the knack, others don't.
So i suggest, as a technical exercise, asking a friend to pose for you. Don't try artificial light, but aim to shoot for an hour or so, in one place - near a north-facing window will be good, avoiding too much contrast.
Your street shots were great: build on that sort of instant working relationship. If you can approach strangers, working with a friend will be easy. Set the technicalities in advance, and concentrate on the look, the character, and maybe a few set-up poses - hands included, or using a prop (I've had repeated excellent results with an old micrometer, and some engineering and building tools from a car boot sale).