I still play with a masters team.
Outside of practices, you want to focus on leg and core strength - so do dryland and water exercises that emphasize those. Squats / Lunges / Plyometrics, and ab work for dryland... you could do weighted egg-beater drills in the water (the class is fill a large water cooler bottle and try to lift it while treading, while it drains).
You can also work on ball skills, so just passing a ball against a wall, or passing with a partner in the water.
Endurance is also key, so for dryland, go for long runs, or do swim sets in the water, mixing sprints with longer yardage.