A lot depends on what the travel involves. Maybe all it takes is coordination on location and dates. Maybe it's a question of one person doing a bit of research. But, some considerations:

1. Have clear understandings about costs. Alcohol, expensive restaurants, car services -- all of those are things which some value and others don't. People have different economic circumstances and it's terrible to put both those who may be flush and those who are not in awkward positions.
2. Don't lay out your own cash. This is how friendships end. If there is a need to pool some deposit or payment, have everyone send in their share before you lay anything out and make it crystal clear that there are no refunds for any reason unless you yourself receive a refund.
3. If you are making group arrangements, use an experienced and trusted TA. While they will likely take a fee, they can also save you a good deal on many items. They can also play the bad guy if it comes to it.