As I recent Linux convert I am learning how to make the most of Gimp after years of using Photoshop, Paint.NET and the Snagit Image Editor in Windows. Gimp is a very capable graphics editing application, but it takes a bit of warming up to.
One of the ways to get more out of Gimp is by taking advantage of it's Custom Keystroke feature. Start in Edit -> Keystrokes.
Now enter keystrokes for your most common used tasks. I do a lot of stroking and resizing, so I added a simple "S" keystroke to launch the stroking dialog box. You can also use custom keystrokes for duplicating keystroke processes in other graphic design applications with which you're familiar, like Photoshop for instance.
You'll be surprised how much more productive you'll become in Gimp with a few keystroke settings.