Given the vagueness, here’s a couple exercises.
Chins. Work up to 15 over several sessions, add weight, work to 15, add weight, repeat. Add at least one rep per session that you don’t add weight.
Bent over curls. Literally, bend over at your hips, and do curls. You can do these one arm at a time bent over a bench. 3 sets of 12-15.
Slight Decline Bench press. Put a plate under the foot of your flat bench. Do 8 sets of 3, then drop the weight and 6 sets of 8. 2-3x a week. If you have a place to do dips, you can do the sets of 8 with the dips.
Seated Overhead Press. Sit upright with your feet supporting you, and no back support. 5 sets of 4-6. When you hit 5x6, add weight. Then do Partial Wide-grip Upright Rows, raising the bar from arms straight to the bottom of your ribcage. Hold for 3 seconds at the top. Do 3 sets of 6-8. Add weight at 3x8.
Finish that with a single set of 20 lateral raises with a weight where the last 5 reps should be nearly impossible.
Squats OR mid-shin rack pulls for 5x4-6.
Do all those lifts 2-3 times a week; chins 3-5 times a week.
One way to put things together:
M: seated overhead press + pwur + lateral raises; rack pulls
T: chins + curls
W: decline + dips; squats
R: chins + curls
F: overhead + pwur + laterals; rack pulls
S: chins + curls
Rotate the overhead/pulls and decline/squats days next week.
If you’re not making progress every session in either weight or reps, fix your diet. If that still isn’t working, add in another rest day and spread things apart a bit.
This is just a “I wonder what if”/guinea pig routine. Adjust if you need to, but there’s a starting point.
The emphasis is on 1) chest [slight decline for most of the chest, overhead for the upper chest], 2) arms [lots of pressing at different angles for the triceps, weighted higher-volume chins for the bis], 3) width, via shoulders [seated overhead presses, partial rows with the held contraction, and pump set of laterals] and lat width [chins], and 4) ab strength [unsupported seated overhead presses, rack pulls and squats]. This, combined with a good diet, should do a lot toward making you look more beach ready. I’m fully expecting your form to be kind of bad, and for that to work in your advantage.
Since I know absolutely nothing about you, how you’ve trained in the past, what you know or don’t know, what you currently look like, your current frame, etc. etc., this is pretty much a shot in the dark. Not that I’m a trainer or anything anyway.