To me nothing says summer like a day on the beach. Instead of waking up at O Dark Thirty in the summer just to use the gym, the beach is a great place to get in some exercise in the fresh, salty air. My personal favorite is to get in a few hours of beach volleyball. But like summer swimsuit season, beach volleyball season must be prepared for months in advance.
Like any other sport, physical training needs to be stressed first, exercises which help build coordination, strength and endurance speed up learning the fundamental skills because you can practice longer and with better form because you're not tired. Using your gym time wisely now and play better on the beach.
Leg exercises like squats, and lunges (forward, backward and side to side) help your bumping skill and vertical jump. Core exercises help your stability. You'll be playing in sand so using the BOSU ball to help build ankle strength and endurance will reduce risk of injury. A big drawback with playing in sand is your vertical jump won't be nearly the same which will restrict your spiking and blocking technique, leg and core exercises will help when using the proper techniques.
Finally, practicing on the indoor courts during the winter/spring will help build those fundamental skills as well as being a great way to burn off calories.
Last weekend I spent Friday night, Saturday and Sunday on the indoor courts for a total of 15 hours and burned over 7000 calories. That's the amount of calories in around two pounds of fat. Fat I won't be needing on the beach in the summer.
Good luck to all you dietbetters on reaching your goals.