So many theories out there...

Is it just playing scales slow at first until you get them clean then gradually day by day, week by week, month by month speeding up?

What was your method of building good, clean speed?

What has / still is working well for me is developing a synch between my fretting hand and picking hand.

If you can tremolo pick cleanly and play legato fast, there's no reason why you can't develop better alternate/econo picking.

I'll build up speed legato first, then work in the picking until it's fast. One side, then the other. If I try both at the same time, I feel like there's this final "jump" in speed that I can't do.
Practice slowly at a speed where you can play clean. Do that alot and then practice slightly faster. Keep practicing faster until you get to the speed you want.

Also, practicing legato and tremelo picking separately helps too.
Speed is the crack of the guitarists of this generation.
Nevertheless another unorthodox suggestion which has given me results without actually wanting to develop speed, try practicing it insanley slow, then play it at a comfortable level, and suddenly speed it up insanely to the max you can.. keep doing it, keep cleaning it up.. and then go back to practcing slowly.. works faster in my limited experience (always keep your technique tight and good)

But do what works best for you.
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