Nice try for the first tutorial... As 9ReMiX9 said, you should use some brigter colors, at least for the dirt block, the background is fine to me, but dirt could be highlighted abit more, with either the brighter color or some extra effect... You could also do a more 3D view by making the edges of the dirt with corresponding shading (light/dark) if you know what I mean ;) but nice effort, DIA for you.

Looks good so far but you should improve on a few things. First one, define some of the lines more. Second, along with defining the lines you should add more of a separation in the background because it looks like it is blending in. Finally brighten it up a bit. Not by using the contrast tool but by going over the colors more with either a brighter gradient or replacing with a brighter one. Using the contrast tool will add too much white and you don't want to do that. Overall, a good job though.

Nice

I love this. I am a total Newby at using Gimp/Photoshop ( I prefer Gimp) and this is very well done. I like how you did this. Thanks for the Information bro. (Subbie For you)