I can see what you were going for here, and the blue and yellow tones in the fringes of the sky are great against the black cloud.
Still, I think the sun dominates the composition too much. It's a massive blob of over-exposure (that viscious white colour) in the top center of the frame. I think the real problem is that the photo might have been taken whilst the sun was too high and too bright. Others can probably guide you better, but there's truly no shortage of sunsets in the galleries, it might be worth looking at some good ones to figure out when to take the best photos. Waiting half an hour an hour here, I feel, would probably have paid dividends.
Other quick tips for this kind of photography
- rule of thirds - a little overplayed (in my opinion), but generally its better to put things on the thirds. Your camera probably has a setting which will show you where the thirds are in the viewfinder. Lining the horizon up with one of the thirds will make it look a bit more balanced. Also, using the guidelines will help keep the horizon straight.
- if the colour of the sea isn't that flattering, try to leave it out as much as possible. This could mean putting it on the bottom third, but in this picture it might have actually been better left out almost enitirely. Kneeling down then zooming in so that the cusp of that back wave and a narrow slip of the sea is all that was visible could have helped. As it is, the sea is very dominant but its also gray not as interesting as the sky.
- finally, if the sun is bright in the sky but very low like this, whilst you're waiting for it to get lower, try turning around and shooting some stuff on the beach instead! The sun has different coloured light at different times of the day, and at this point late in the evening it will give everything a stunningly warm tone and long, interesting shadows.
Hope that helps.