In addition to tanning, which really does help, if you’re a hairy guy consider some manscaping. Waxing your back is a social good, you know, but waxing your chest can make you look a lot more defined as well. Between the tanning and the waxing you can really look a lot better without having actually changed your body at all.
Oh, and while you’re at the beach (and this is kinda difficult) avoid eating a lot of salty foods and beer and carbonated beverages and things. Makes you retain water. It always sucks for me when I work out to get all ready for bikini weather and then I go to the beach and eat fried pickles and drink beer and have to suck it in a bit. 