Contrary to what pop culture would have you believe, building a beach body involves something other than engaging in activities that can be done on a beach. In fact, most of us require heavy exercise that's done in a gym to develop head-turning beach physiques. Furthermore, such exercise must be progressive so strength is substantially increased.
Non-beach exercise for a beach body
Body-weight exercise, like those that can be performed on a beach can build solid bodies if progressed far enough. For most, however, sufficient versions of body-weight exercises (1-legged squats, 1-arm pushups etc) are too difficult to be progressive with. In order to meet the requirements of sufficient tension and progressibility, most have to weight train; and weight train using exercises that allow for adequate force output.
Exercises that allow sufficient force output and progressibility for most are usually versions of pushes and pulls for the upper and lower body. In fact just one push and one pull will suffice for the upper body while the lower body can be developed immensely with as little as one squat variation. An example of such an abbreviated, yet effective workout could be bench-presses, pull-ups and barbell split-squats.
The aforementioned abbreviated workout will cover strengthening most of the body while allowing for effort and progression to be concentrated on just 3 exercises. The bench-presses will ensure sufficient chest, anterior shoulder, and triceps stimulus. Posterior shoulders, upper-back, and biceps redeem a lot of tension from the pull-ups; while the split squats hammer the hips, thighs, and low-back.
Progression for a beach body
Once progressible exercises are decided on, focused progression must be implemented. For initial "gains, adding weight/reps whenever possible will suffice. Beyond the intermediate phase, however, more creative progression strategies must be exploited. Strategies like progressive force with fixed loads, escalating density, as well as progressive range of motion might prove to be helpful. In any case, utilize diversified progressions when generic progression fails.
A diversified progression schedule often involves a rotational order of strategies each utilized until it stops working. Two to three weeks might allow for added weight to yield success. The following two to three weeks might allow for added reps to the last sets to be successful; while the following three weeks involve progressing via faster set/rep completion.
Development of a beach body isn't going to happen hanging out at the beach. Forging the solid musculature that turns heads at the beach requires most to routinely perform heavy squatting, pushing, and pulling movements. To boot, one must get a lot stronger on said movements to substantially change her/his body!