graduated filters in software like LR work best on items that are blended on straight lines that are of the same tonal value. therefore they don’t work well on people.
Your focus is way off. Everything seems slightly unsharp, except for maybe the rock. You camera could be back focusing a little bit. On canon camera’s there is a way to calibrate the focus for each lens. I don’t know about your camera since it’s a nikon. It could also be the lens. I think you might have a smudge on the front or rear element b/c there is a little hotspot on the right side of your image where the water meets the sand. This could also account for the lack of contrast overall. You also are very overexposed.
Here’s a variation i did very quickly and roughly. I brought everything down, made background a tad more contrasty and darker than the rest. Made it a little warmer overall, and did a little high pass sharpening (although I don’t really think that helped much.) Also cropped but kept it horizontal. I think it looks nicer that way.
(once you are done and you want to delete it, you can click here: http://imgur.com/delete/PSjc6Lcmxo1wi19 )