I'm using GIMP and Wacom Bamboo Pen tablet. A typical comic goes like this:
1. Load template. It has 4 panels and all the layers I need (words, frame, sketch, background) plus some layers I don't need but cant be bothered to delete.
2. Come up with the stupidest joke I could come up with.
3. Draw characters standing there. The characters are simple shapes so it doesn't take much time.
4. Draw speech bubbles. Scribble words with ink tool.
5. Add horizon, some trees and some clouds in the background. Note: many webcomic artists forget to do this part. IMO, this is just lazy!
6. Done!
Usually takes 15 minutes or so. However I also like to diversify things a bit, so last few comics took longer than that.
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BLUB CHEESE!