writing Guitar tunes

I find that it works pretty well to hum a tune that you like in your head and then get it down on guitar. Or what also works for punk rock etc. is to use bass setting on a keyboard and see what you come up with and then put it to guitar :S works for me

What I often do is work out a chord progression or a scalar run in standard EADGBE and then work though it with different tunings. Sometimes it sounds pretty freaky, sometimes just wrong and at others plain inspired. If using an electric combine this with experimenting with tonal control, effects units and anything that comes to hand. For my money, you cant go far wrong with a flanger.