Check out some of those if you haven't already, or maybe Digi will help you out a little. He's the resident Gimp gaffer. (In more ways than one, Ooooooh.)
And there's a nice thread called "Sig advice" stickied to the top of the forum, there was no need to make this thread.
This thread (also pinned) has links to tutorials for various programs, gimp included. The one Barker mentioned is more for peer-advice.
As for being the gimp guru, I've actually been using PS for close to a year now...before that, I had taken gimp farther than most ever do though, so if you have specific questions feel free to PM me. In general though, you just need to read a bunch of tutorials, practice with random functions of the program, and look at good sigmakers on this site for inspiration and guidance.
Please check the stickied threads before making a new one...there's the resource thread, which has links to tutorials, the help/tutorials thread, and the advice thread.