So you want to start writing riffs. Whether you use a program on a computer or the old fashioned tape recorder and your noodle, describe your process.
going for a particular style:

1. listen to songs of the genre
2. smoke
3. start hearing similar music in my head.
4. figure our the riff in my head.
5. play it and refine it until i like it.
6. record it.

random creative riff for my own songs:

1. start recording.
2. start playing and riffing.
3. keep playing until i hit a riff that I like
4. play back the recording
5. refine the riff
6. record it for reals.
7. repeat until a song is done.

It seems like a lot of steps, but I can generally write a song on the spot without pre-composing it. and after writing it refine as needed.
All the times I've sat down and said to myself "I am going to write a riff.", I never wrote anything good. But when I play counter-strike or something and die, I pick up and noodle a litte, and sometimes something really good comes out. Then I write down the riff in GP, and play with it at a later time.
Quote by CoreysMonster
Why, my pasty danish cracker, I believe you've got it!