1. Be very thorough is setting your powder measure. I always throw 5 charges together, weigh them, and divide by 5 until it is set correctly. I do not trust weighing only one charge. Double check by throwing and weighing 5 more charges.
2. Always charge all cases in the tray at once, and inspect each case using a flashlight to see if there are any apparent over or under charges - inspect twice before seating the bullet.