The best way to create sigils is just to play around, like a child in art class. These are specific symbols of power for you; no one else needs to be able to recognize your intentions for these symbols so don’t worry about perfection. There is no right or wrong. (From www.bewitchingways.com )
Just play around, let your creativity show, and remember that, technically, (Ahem), you don’t need to use all of the letters. One of the steps crucial to the visualization process is minimizing the image to a small glyph and cutting off the rest. Check out Tsondru’s really helpful link in the first post for additional assistance.