Well I have been playing for about a year(but I have been taking lesons for a short time) I can play some real heavy stuff like,children of bodom,lamb of god,etc. But when I try to create songs of my own I end up with a simple song with just power chords. I want to make riffs like COB and LOG I dont just want power chords all the way through,I want to do some Avengend Sevenfold style Guitar harmonies also. But I dont know where or how to start breaking away from the same power chords. Is there anyway to help me break the evil power chord habbit?
Yes. Learn some music theory. Start by learning the Major scale. Don't worry about modes or arpeggios or chords yet. Just learn the basic Major scale. The learn the basic Minor scale. Again, no modes, nothing complicated. Just learn how to play the Minor scale. Learn some simple theory about the Major and Minor scales. Then mess around with them until you play something you like. A lot of really good riffs are based on the major or the minor scale (in metal, it's almost always the minor scale). Similarly, a lot of riffs happen by accident.
the best ways to harmonise lead parts are using 3rds and 5ths as these are the most common in metal. if you don't know what they are, this refers to music theory, learn the basic principle of intervals if you haven't done so already