The best way to begin alternate picking is to simply play steady down-updown-
up patterns on an open string. If you can maintain a steady rhythm and experience no glitches or hesitations in either direction, you’re doing well.

However, many people initially have trouble making their upstrokes as smooth and loud as their downstrokes. This is natural, because you play many more downstrokes in guitar than upstrokes. Also, upstrokes go against gravity and require a little more effort to maintain smoothness all through the stroke. Just keep practicing, making sure that your upstrokes come up with the same swift confidence that your downstrokes have.

Don’t think too much about your pick strokes, though — simply play as much as you can with a pick, and your picking will be smooth as butter in time. Smoothness in picking is the same as achieving gracefulness in dancing or skiing. You get there by doing it — over and over.