IMO, how to get a good signature on gimp.
Render ; Saturate, Contrast it, Color it ... nothing too severe though or it will wreck the image
Shadow ; I like shadowing my render, this can be done by a blurred image or whatever
Render ; Bigger render. 40%-ish opacity? Mess around with the modes.
Brushes for Background; They add a background to the pic. You can download photoshop brushes at brusheezy.com/ and install them.
* HOW TO INSTALL *
You'll need to have winrar or some extract program to do this. If you need one, mail me. Once you download the brush, go to dowload.
Right click on the brush and click 'Extract files', after ... a folder named the same will pop up.
Once in Gimp, go to Edit > Preferences. At the bottom it should have "Folder" There should be a small + beside it, click on it. It will scroll down 'Brushes', 'Text' etc. Click on 'Brushes' and the screen to he right should change showing 5 small icons and a bar with 'Browse' beside it. Click on the first icon to the right (a folder picture) and then, click 'Browse'. You should be able to make it to 'Downloads' from there. Click on the folder you extracted and click 'OK' on the brushes screen. It may say you need to restart GIMP, go to File > quit and restart the program again. They should be in your brushes section. Done.
Text ; can be got from dafont.com/, installed the same way as Brushes except when you click on the + beside "Folder" go into text and install them there.
Fractals/C4ds ; can be got from planetrenders.com/. I advise you set them in a different mode than 'Normal' to avoid the fractal/C4D taking up too much attention.
That's really it, if anyone wants GIMP tuts, I can give them ones to suit their level in graphics.
Here's two I made this morning (only because I was sick). Keep in mind, I'm only advanced intermediate/intermediate.