Tips to get you started:
1. Plan your itinerary. Will you be walking all day, everyday? Lounging at the beach? Enjoying dinners out? What will be filling your days up?
2. Check your destination's weather for when you will be there. Rainy? Don't pack your leather shoes or jackets that aren't waterproof. Gloomy? Layers will be key. Windy? Plan on no hats and chic hair situations to not look crazy windblown Hot? Think loose fitting and light fabrics.
3. Check out your destination's color pallet. This may seem odd but if you dress with the pallet of your location in mind you will always look perfectly chic in every photo. This will also help you keep on track with a cohesive packing color pallet to allow to mixing and rewearing items.
4. This is always something I think about too... I like to eat and enjoy myself on vacation so I purposely avoid tight fitting outfits so I can be as full and comfy as needed. I may add a belt to cinch in my waist for some shape or a fitted jacket but I keep my outfits loose fitting for the most part for my eating!
5. Decide on hair looks. I wash my hair about once a week so I plan accordingly. I usually start my trip with fresh hair then plan for hats and accessories like headbands and clips for the rest of the trip so I can avoid traveling with a million styling products. Dry shampoo is the best and plan for wash and wear styles like cute braids. If you must, plan on one curling iron to touchup any simple styles.
I have sort of a fool proof science when it comes to my packing. I go day by day and pack for the whole day each day at a time so I don't forget something. I visualize the day from start to finish and pack literally each item as I would envision using it per day.
With this structure, I rewear a lot of items. I pack two pairs at maximum, one jacket in a neutral color, one pair of sunglasses and one hat. One beach tote that I use as my carry on and one crossbody bag to keep hands free. I also try and pack my swimsuit cover to double as a shawl for chillier evenings.
This is how my packing would look for a beachy vacation with mulitple different additional outings: