I went on one by myself several years ago and loved it because I met lots of interesting, fun people and about 1/3 were also there by themselves. The procedures for the one I did were very focused on safety. We boarded late afternoon and then one of the dive instructors interviewed everyone, looking at our dive logs, etc., and then paired up solo divers based upon this info. Before every dive we had an in-depth dive brief about the site. There were a couple of people who paid a bit extra to do dives with a divemaster. Throughout the dives, there were always a couple of divemasters down there to point people towards cool things.
The crew was fantastic - extremely helpful and fun. I had pre-paid with a cc and was able to add their tip on at the end. I guess the obvious is several swimsuits, towels, a hat and lots of sunscreen. Make sure you have lots of reading material for the downtime between dives.