there are many ways, but it also depends on the composition of your participants. I taught water aerobics for 18 years, and my participants – for the most part – were women in their fifties and up, often with conditions that made water aerobics their only option, but some of them also in quite good shape from years of water aerobics. Many were overweight.
I found that the right music can make all the difference in the world. Broadway hits were very popular, and I often ended up with a sing-along.
I noticed that partner exercises were not popular in my group but that fast directional changes often made the whole group chuckle because it threw them off kilter. A beach ball to play some form of ‘volleyball’ was popular but it can exclude some participants. I also used water noodles in a variety of ways.
Depending on the rapport you have with the group, it can be helpful to have one ‘buddy’. I rarely corrected directly unless there was risk of injury but I would single out a person as a good example and made an effort to spread the praise around.