Sibil has a point--you do have to kind of collect a series of ideas, suggestions that leaves you able to adapt to the crew + environment that you're dealing with. Some of the ideas I have work really really well with certain groups and fall flat with others--it's often a matter of being able to get a good read on the people you're dealing with.
As an example, I noticed early in one of my weddings that one of the groomsmen was bursting out in song, spontaneously. I then had an idea that I tucked away until the bridal party session. In short, I had the guys choose a song and 'perform' for the ladies (who fawned / made fun of / thumbs up'd etc.)--the song didn't really matter, but their performance was awesome and it showed in the images. I did not have to pose them at all--I just offered up the idea and they responded really well whilst I grabbed candids of the proceedings.
In short, I prompted them to engage in some activity that not only introduced drama and expression to the photos, but also allowed them to have fun, and, in this case, reveal their goofy playful personalities. My recommendation is to think of other kinds of activities that you can suggest.
Other than that, though, you really have to go into this kind of session with a bunch of pose ideas--more than you need. I usually go into a bridal party shoot with about 15 distinct ideas in mind; most of the time I only have time for 8-10.