The Artist's Guide to GIMP: Creative Techniques for Photographers, Artists, and Designers (Covers GIMP 2.8)
5 GIMP Tips from the AuthorLike things just so? Your favorite Tool Option configurations can be saved as presets. Use the buttons at the  bottom  of the Tool Options dialog to save, load, and delete presets.Color tools can be added to the Toolbox using the Preferences dialog. Go toEdit>Preferences, then   select Toolbox.Need quick access to layer functions? Right click on any layer in the Layers dialog.Hold Ctrl when using the Rotate tool to rotate layers in 15-degree increments. Likewise, holdShift+Ctrlwhen using the Paintbrush tool to draw lines in 15-degree increments.Using full-size layers when you don't need to can slow GIMP down. To remove transparent and unused regions of a layer,   select and copy the area of interest and paste it into a new layer, then delete the original layer.