Well, other than what you've said before, it's obvious you are a beginner, so instead of telling you to use tutorials, I will try to give you some advice myself:
- First of all, try to make things look more realistic. That is use materials and grounds that are looking good with one another (by colour or just a feel).
- Second of all, use the Doodad Palette - add green trees, grass tuffs, bushes and stones. Having boulders stand out like that isn't looking very nice.
- Don't build 'square' (in fact rectangular) buildings. That looks just so 'out-of-date'. Try being a bit more initiative with the shape.
- The coastline has to be much more random. In nature, you would never see a naturally occuring perfectly straight coastline - make it a bit more rough and random. Nature is more chaotic and that's what makes it a good thing to use in mapping.
- Try looking through mapping advices and other poeple's threads (and tutorials of course) to see how they manage to join all the components of the map together.
Other than that? Pracise, practise and practise.
Regards
Sey~