Check out this alternate picking exercise. The exercise is actually several exercises using different combinations or finger orders with the fretting hand. The idea is to use pick strokes that alternate down, up, down, up. The best way to maximize your economy of motion is to mostly use the wrist to move the pick up and down while keeping your pick gripping fingers still. Your elbow should not be active either. To really make sure that your are keeping time properly this exercise should be done with a metronome. Start slowly and make sure each group of 4 16th notes is played evenly from tick to tick. The first note in each group should "disappear" into the tick. Keep in mind that you can move these examples up and down the neck to be played on any 4 consecutive frets.