for me..how i improve my alt picking is by playing 3 notes per string scales..or something...forgot which vid i watch...he came out with this 3 notes n 4 notes per string exercise...

for the 3 notes per string...i normally play the 1 note louder...so it goes 1! 2 3(!= louder) n repeat..

as for the 4 notes per string exercise it goes 1! 2 3!! 4 (!! = softer then the 1st note)

if u get wat i mean..its easy to do it ascending..but decending is a lil tricky..took me a while to get use to it...then basically chromatic scales...up n down...er...yea..use a metronome..i start with 60 beat...which is real slow...then work my way up..if u can reach 200..its a quite fast ...but im no where near it.haha
good luck