So i am a huge fan of technical Melodic death metal style riffs. Things such as Keith Merrow, Jeff Loomis, Omnium Gatherum, Insomnium, Lamb of God and the black dahlia murder (just not the vocals). I mean, i can play all of it, but i cannot write anything to save my life. Anyone got any tips or anything to practice? or even any more bands/artists in a similar vein.
Well, can you think of a riff that you would like to play that doesn't yet exist, without a guitar in your hand? That's where you should start in my opinion: think of something to play first, then figure out how to play it.
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Take one of their riffs. Change a note. Then change the beat of another note. Then change a second note. Then change the beat of a different note. Now take that, add your own feel to it. Now you have a different riff. Do that enough times with songs and you'll start figuring it out in your head. I don't play metal but half my riffs are something I heard on radio then hours later tried to make something sound like it, then boom something different.