well, I'd say you should start with basic stuff like color gradation in the sun, sky and water. clouds too, now that I think of it.

think of the sun as a lamp, then make it gradually darker from there. there's a tutorial on how to pixelate around here somewhere (the forums); in there you can various types of patterns to use in color change.

also, try to select a palette and stick with it.

hope it helps.

is it better?

my water is so static, i dont know how to make them feel more like a real water

Yeah definitely use references,  they help so much.
So basically I made a color edit for you.

First off, 600x600 is giant. You don't want to be making a scene that large it will take forever. I reduced it by 50% but 300 by 300 is still really big. I would suggest a 150 by 150 to start.
When you look at the sun, it's not an orange ball. It's so bright that you can't even look at it. I would also move it a little bit farther above the horizon for a beginner, you don't want to get into sunsets yet. Everything turns red purple and orange its crazy. As for the water, I wouldn't worry about motion right now, get the basic shades and colors down first. Ok so, as an object moves farther away from you, the atmosphere gets in your way. This gives the object a tint of whatever color the sky is. In your case, you want to farthest out what to be brighter and duller, because the sky is bright and dull.  Go outside and look at a far away mountain (if you can)
They aren't deep green like the grass and trees, they will be desaturated and have a blue tint to them.  Good luck with your piece!