Tiger Fang, are you using MapMaker to make your maps, instead of polyworks? I suggest you use the latter, it's much easier to work with. You don't need to memorize a bunch of wacked mouse + keyboard commands, it's kinda used like Photoshop. With tools on the left and a color palette, etc.
What you really need to do is focus on your polygon's shading. As I can see, they have matching colors, but the corners don't line up with each other in a way that they would match, that is what leads me to believe that you are using MapMaker.
Also, you are using a lot of the same scenery next to each other, try to use some variety. Don't stick to the same thing over and over again, that is one of the things that makes map dull. Expierment with different sceneries, colors, and levels of opacity.
As for the texture, there are hundreds to choose from, but trying a few and seeing which works best from those is an okay approach.
I wish you luck. Feel free to ask us any questions.