You need a reference point so that you can consistently find the strings. Rest your forearm against the edge of the guitar body, or place the edge of your pick hand on the bridge, on the side oposite the pickup. (You might as well learn palm-muting while you're at it).
Once you have a fixed point to work from, you can develop your 'muscle memory' because the same movement will always bring your pick to the same string. Finger-pickers often 'anchor' their pinky on the pick guard, or their thumb on the guitar body.
I would not recommend using a mirror for this practice. You want to train your hand and arm muscles by [u]
touch[/u]. Adding mirror-view hand-eye coordinaton will just make it confusing.
Lordathestrings
Guitar Tricks Moderatorwww.GuitarTricks.com - Home of Online Guitar Lessons