What has helped me is learning songs that I find that fit my style and breakdown the form first. Like the riff is simply called "The RIFF" then there may be a verse form that I would call "Verse" then a "Chorus" then "Bridge" etc. This may give you ideas about structuring a song. Keep writing even if it's just riffs - some ideas may spark others that can be put together at a later date.
Keep working the creative mind!

All the best,
Joe Pinnavaia
http://www.guitarlessonsbuffalony.com
http://www.digital-nations.com/artists/testtuberhino