Now I've got a cool little exercise. Try adding a rest (or rests) in your 16th note sequence. Here are some examples:
When you execute those rests, use 2nd and 3rd finger of your fretting hand to damp the strings at rests. This way you don't have the bass sound on the rests, though, this is the matter of taste. Make at least 10 more, and loop them. Feel free to use any time signature you want. Try to combine your licks later on. You might come up with some really groovy riffs, or even song ideas! Now try playing all of this only with upstrokes. I suggest you go for it with tempo around 90 bpms. Next thing you could do is add the 5th and an octave to those E's, so you get power chords. You can maybe flatten the 5th, so you get the really harsh E(5-) chord. Add the open G string to that chord, so you get the Edim chord. It's sound is perfect for crankin' your amp to 11 in 5am and waking up your girlfriend, especially if you don't want to see her sleeping over at your place anymore! :) Let's play with note lenghts a bit. If you use 32ths and 8ths in the riffs, you get a plenty of new options. 32ths usually build the tension and 8ths lower it, so always tend to have a balance between the both. Let's just experiment for now.
You should create at least 20 of your riffs. Right now. Take 5 of those that are best. How do you know if they're best? Very easily. They make you headbang! We'll make them more colorfull by adding more notes. Use phrygian scale for now (though, you can use variety of others), to keep that heaviness. It goes like this: I
'm sure you get the point. Anyway, that's it for now. Experiment with those ideas a lot, and absolutely positive that you're gonna end up with dozens of cool riffs. I'm going to talk about this subject on few next articles, so stay tuned! And keep your heads bangin'!