Watch the Picking Considerations 3 online guitar lesson by Bruce Arnold from Guitar Physiology Survival Guide
Since there are so many ways that students mess up their picking I should mention a few of these for troubleshooting purposes. Watch that you aren't picking at a vertical angle to the string, that is, picking away from the guitar. This is a common mistake and will greatly slow down your ability. Beginning students will commonly pick all notes in a down stroke.
If you are a beginner try to move into alternate picking as soon as possible to avoid having a habit of always picking downwards. Students also tend to over accentuate notes. The more you can play with a consistent attack the smoother your playing will sound. You will find this across the board from beginner to advanced players that have too much variation in their attack of the string which causes their playing to sound uneven.