At OSDS, once per night, we usually do a celebratory jam. It’s traditionally for people celebrating their birthday (usually in the same week), visiting from out of town, celebrating an important event or leaving for/coming back from a long absence. (Let the host making the announcements know what you're celebrating.) The people being celebrated go inside a circle formed by the other dancers (or in the case of a live band ideally a horseshoe shape as the band forms the rest of the circle) and people try to “steal into dance” with them (they are often called steal jams for that reason). Everyone whether witnessing or jumping into the circle is participating! Support the jam by clapping to the beat. Vocally appreciating any especially cool moves, or especially smooth/cool swap ins or outs. Moving supportively with shuffles, stomps, doing basic solo jazz steps while watching the action of the main jam dance.
The spirit of a celebratory jam is to celebrate the people inside the circle. It is not your moment to try to show off. It is all about them, making them feel good and giving them a moment to shine. Everyone wants to feel good during those jams. No one wants to get stuck with only one or two partners. If you notice that they don't have a great deal of people trying to jump in please take it upon yourself to get in there! While you're in there, introduce yourself, let them know its nice to meet them or something nice like that and/or congratulate them, welcome them back, wish them a happy birthday, etc. whatever is appropriate and/or congratulate them, welcome them back, wish them a happy birthday, etc. whatever is appropriate - basically be nice.
If you want to go into the circle, it's good to observe how it's done before jumping in. Be careful not to hurt anyone when trying to steal into a dance. It is customary to wait for two eights of music before stealing. (Being able to count musical phrases can take some time so just make sure to not steal a dance right after someone did it.) Consent is not as obvious here because people being jammed do not get to choose who jumps into a dance with them. Be mindful of that. Do not use this as an opportunity to dance with someone you know does not want to dance with you - for example, because of a personal conflict or because they have said no to you earlier that evening.