My favorite hints and tricks for the GIMP

Sharpening an image
Removing red eye
Making image backgrounds transparent
Draw a straight line

Sharpening an image
1.Click on Filters -> Enhance -> Unsharp Mask

2.Start with the following settings and adjust until you are satisfied:
Radius - 1.0
Amount - 1.00
Threshold - 0

3.click on Filters -> Enhance -> Sharpen and adjust until you are happy.

4.Save your image!

Removing red eye
1.Zoom in on picure until the eyes are large enough to work on.

2.Select the Dodge/Burn tool.

3.Choose a Circle Fuzzy brush that is suitable for the work area. I like the brush to be about as large as the pupil is. I find that a #5 brush is usually just about right.

4.In the Dodge/Burn tool dialog box, expand the Pressure sensitivity and check the Opacity & Hardness boxes.

5.Center the brush on the red eyes and click the left mouse button enough times to adjust the eyes.

6.Save your image!

Making image backgrounds transparent
1.The image must be a GIF image. If it is in any other format, open it and then export to a GIF image.

2.Layer -> Transparency -> Add Alpha Channel

3.Choose the "Select contiguous regions" tool

4.Click on the area you want to be transparent

5.Edit -> Clear

6.Save your image!

Draw a straight line
1.Open or create an image.

2.Select the Paint Brush tool.

3.Choose the appropriate brush size from the Tool Options dialog box.

4.Click the left mouse button and hold, on the image where you want one end of the line to be.

5.Hold down one of the Shift keys on your keyboard.

6.Move your mouse pointer to the location where you want the other end of the line to be, and release the left mouse button.

7.Release the Shift key.

8.Save your image!