Often the key to increasing speed is really slowing down and looking at every tiny detail of your technique. Are you cleanly fretting the notes in the best possible location with each finger, each time? Is your posture clean and healthy? Are you striking the string consistently with the finger/pick at the right angle of attack every single stroke?
It's easy to play fast and sloppy up to a point, but then it takes clean technique to take the next step.
Priceless.