Chromatic exercises (1234, 1234, or 123, 123 etc) up and down the 6 strings to get the rhythm of alternate picking (left and right hands working together in time while picking up and down). Then a lot repetition of the scalar patterns to get muscle memory. That's the only way to get fast. Out of time speed can be achieved easily, don't fall into that category. Play as fast as is comfortable to a metronome, continuously increase the bpm by 5 whenever you can handle it. Eventually you will hit high speed with accuracy.