Working with a metronome is generally one of your best bets if you're looking to build pure speed. Practice 16th notes at, say, 156, until your hand gets tired. Take a very short break, speed it up, rinse, repeat.
If you're practicing licks from actual solos you're learning, do the same - slow then down using a metronome, or Audacity if you have access to a computer, and practice it until it's entirely clean. Then speed it up a little bit at a time.
It's all about putting in the work, really. You want to get faster, you practice to be faster. There's no good substitute for it; the same principles as weight lifting.
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