Throughout the ages of all things guitar (metal, alternative, punk, country) there has always seemed to be a pattern to the riffs and solos. Such as intro, verse, chorus, verse, chorus and so on. And after a while you have to admit that it gets predictable, and sometimes mind-numbingly boring. This is an opinion, so you do not have to get mad because you think I am telling you what's wrong or right. If you are in a band, thinking about starting one or playing just for fun, do you really want all of the songs sounding the same? Well, if the answer is 'nay' then listen up!
When writing a riff, remember this: don't go with it for long! Once again, this is an opinion, im not saying it's wrong nor right, its just a guitar technique for anyone interested in variety. When you write a song, try to change the pace, the speed or even the instrument being used, for example: you could start off with an intro performed by a keyboard, any wind instrument or any other string instruments such as viola, cello and so on. Then come in with a catchy guitar solo/intro. After you've made a dramatic introduction kick in with the percussion, bass or even another guitar doing the rythm. Most songs hit the chorus within 30 seconds of the verse. But I have found it creates and element of mystery to "skip" it. For instance: intro, verse, prelude and then another verse. The prelude could consist of just an alternative instrument (keyboard, strings, and what not) or just perhaps a solitaire bass riff or the guitar intro again. And after the pre-lude hit another verse. For variety you could also try a different riff, perhaps faster, slower. Just different. You will have people asking themselves "whats next?"
Heres another trick: as the drums beat faster, strum the string slower, if the drums go slower, speed up the rythm of the guitar... its un-expected and shows great talent.
When you get near the end, begin changing the pace, switch back and forth from guitar to an alternative instrument. Perhaps even repeat the prelude, but faster of slower. And end it with something that can catch the attention of the listener. Scratching the strings from the bottom up, make the guitar "cry", or just hit some random chord, its all about variety.
Well, thats all I have to say for now. Just always remember: any person can write a song, but it takes someone with imagination to make it a piece of art.