5. Use unorthodox means.Great riffs are just waiting to be unlocked. however, you may have to do some sneaky things to find them. You can try stretches that you can barely make, and make some good arpeggios out of them, or you can make some odd chords that you don't think exist (which, they do) or play with techniques or styles that you would never use. Experiment.

6. Let your fingers do the walking.One of the best methods, is improvising. You don't even have to be good at improve, you just have to be playing. I have many great riffs made when I was talking to my friends, or watching tv. Just get relax, don't think about it and play. Just play. I can almost guarantee that one day, when you aren't thinking about what you are doing, you will come up with something that sparks your attention.

7. Unleash your emotion.The most obvious method is to play what you feel. If you are feeling sad, play the guitar, and you will most likely come up with a sad riff. A great one to use (especially if your girlfriend/boyfriend breaks up with you; or better yet dumps you. Not trying to be a jerk, but it's the truth.

8. Conclusion.To conclude, I just want to say that, these are just ideas that you may never have thought or overlooked. If you already knew about these, then all the power to you. I hope I have sparked your interest and influenced your composition skills at least a little bit. One thing I didn't mention is to try moving open chords to higher frets. You an make numerous original riffs like this. Anyway, don't give up; you'll find at least one good riff.