For accurate picking use your wrist mainly and maybe your thumb a bit. Using your arm is only good for inaccurate tremolo picking. A good exercise is alternate picking an even number of notes on one string, then hitting a power chord up a string.
e.g. Metallica One, count 1 2 3, 1 2 3, 1 to the beat and use your wrist, not your arm.
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Start slow, practice to a metronome, using different numbers of notes per beat. Try alternating strings at each beat or two. I just got my 3 notes/beat speed up by playing a riff towards the end in Dimmu Borgir - Behind The Curtains Of Night, and Cradle Of Filth - Carrion.
I had to train my brain to think fast enough to count every note as "1 2 3" etc. Some songs like Cannibal Corpse - Sentenced To Burn (after the squealy riff), I have to count 123123 etc but play 2 notes per count.
You have to push yourself not just physically, but mentally to get accurate speed. Increase the speed of your metronome. If you just want to tremolo pick one string at insane speeds, that's just stupid. I can hit about 17 to 18 notes per second; if you want to go faster, then I suggest woofing down a shitload of caffeine. (Also, I tend to play faster at night.)
If you want accuarcy you need to spend some serious time exercising your brain and hands; i.e. the "muscle memory": it is alot faster than your brain memory, but it takes alot longer to train. So don't just play the same easy songs over and over, challenge yourself with songs like off Cryptopsy - Whisper Supremacy (always try to play 4 notes with your wrist, not 3 with your arm, when alternating between strings, and start off slow). Maybe that's not a good example, as I figure their stuff out myself and there are no good tabs.
Sepultura Arise is a good song to learn as it has fast bursts in it. The live version leaves me for dead! Also get your down-picking up to speed with Master Of Puppets, and then move onto some of The Haunted off their original album.
You can do exercises and shit, but for me, I'd rather learn the inefficient way - learn many many songs. www.insaneguitar.com
has some exercises, including legato, sweeping, alternate picking. You don't need to use alternate picking for speed, legato can be faster. Be warned, those exercises are fucking difficult to play (even at a moderate speed) as you need to equally develop all your fingers; get some meat on that pinky etc