Yeah, I agree that starting slow here is the best way to do it. I got fucked because when I started I just wanted to be like Kirk Hammet. And I was able to match his speed pretty quickly, but I was using poor technique, or no technique at all.
So, now I am redeveloping my technique, especially with alternate picking. I am pretty good with legato, really fast I would say, but I suck at alternate picking and it is Kirk Hammet's fault. "You have to downpick lightning fast or you'll never be in this band!"
Sorry, got a little sidetracked.
You just have to start slow, and when you can play it clean and smoothly, just bump the tempo up a notch faster and keep going, this does work!
I have some simple midi drumbeats that I created on my computer, and I just adjust the tempo with that. Its much more interesting than a simple "clicking" metronome.
Pay attention to the "technique" of shredding. If you just try to play fast without really knowing what you're doing you will regret it later in life! Trust me!
Now I found out that I have to learn this economy picking thing too!