Smaller movements, less tension. You want more specific advice then ask a better question.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Try to loosen up your wrist and your elbow. Good advice I got from a professional (Rob Balducci) was to use a wrist brace while practicing alternate picking to help loosen up your elbow and then try to lock your elbow in one place and use your wrist.

Choke up on the pick and keep movements tight. Sloppiness is the last thing we want.

practice on each string both open and fretted at various points of the neck so you can get used to the changing tension as you pick.

use a metronome to keep time.

Start slow and increase speed slightly as you get faster.

Remember - "Slow is smooth, smooth is fast"
Quote by strat0blaster
This is terrible advice. Even worse than the useless dry, sarcastic comment I made.

Quote by Cathbard
I'm too old for the Jim Morrison look now. When I was gigging I had a fine arse.
Of course, everything that other guys said:small movements and tenson free playing. But I have write something from my alternate picking investigation, the way I improved alternate picking for the past couple of months. First of all I isolated the parts- the things that A.P. consists of and these are: tremolo picking, down picking, up picking, inside picking and outside picking. So there are always one of those things that you suck the most and it'll hold you back. I sucked the most at inside picking, and that's why my speed wasn't improving, no matter what I do. So I practiced separately all of those aspects (you can invent your own exercises) and put accent of things that you suck the most. At least that was thing for me
Quote by kimi_page
tremolo picking

This is not a separate thing from the rest of it, it is made up of the rest. 'Tremolo' is sound, not a physical motion.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.