They're not bad really.
Number 2 could do with a little increase in exposure since it is a little dark.
Number 3 is a little dull looking, but that is because the light is very flat.
Number 4 looks a little over exposured in the highlights.
You're right about composition. The same sort of 'rules' also apply to seascape and landscape photography.
The Rule of Thirds and Golden Ratio are often used to good effect within this genre of photography, since it is often easy to break up the picture into thirds horizontally with sand, sea and sky. Positioning boats and other objects in the sea or on the beach at intersecting thirds across the vertical plane also works well (Bear in mind sometimes rules do need to be broken!)
You've clearly got a wide angle lens which will give you the ability to capture those wide open vistas at the beach, but be careful. Although it is great to have such a wide view, you often forget that a wide view of nothing in the foreground is quite boring. It is one of the biggest mistakes with a wide angle lens - a case of look I've got everthing in front of me captured... well yes you have but it is very small and very bland. You can actually use telephoto lenses to get great shots at the beach.
Your 1st and 5th pictures are better because the have something interesting near the bottom to lead the eye in. Using diagonal objects across the fame makes the eye scan across it and can lead the eye to the object you want as the main focus. The pier shots had potential, but they're just slapped across the picture horizontally. Move closer to the pier, place it at a horizontal angle leading the eye into the shot .
Don't be frightened of getting in really close to rocks or other foreground objects (it might mean wet knees and boots). If you can get down a bit lower - as an example in picture 1, move forward a few feet, drop the camera down to a few feet above the water (be careful not to drop it!) and use that rock sticking out to good effect, place it on a intersection of thirds and it probably would have been a stronger image.
Picture 2 I think would have suited a telephoto lens. Zooming in on those lovely sun rays streaming through the clouds and including less sand and less clouds would have been better.
Here are some nice little guides
http://www.exposureguide.com/photographing-seascapes.htm
http://www.genkin.org/blog/index.php/2010/10/19/12-tips-for-seascape-and-coastal-photography-guide/
Lastly some Flickr groups with tons of shots - some brilliant ones, some good ones and some hmmm ok ones as well
You can learn an awful lot by comparing other peoples work. See how they divide the scene up and lead the eye in.
http://www.flickr.com/groups/landcape/
http://www.flickr.com/groups/sun/
http://www.flickr.com/groups/seascapecentral/
Good luck and I'm sure we will all look forward to seeing how your shots develop.
