Think of what you actually need or want to buy, even before the after Christmas sales event. Make a list and be specific, listing model numbers and colors of items.
Go through your list and consider what stores might carry that item. Search online if the store has a Web site and try to plan ahead.
List your items in order of importance. This will help you decide which stores you will visit.
Pay attention to which stores seem to have big Christmas sales. They will probably also have big after Christmas sales.
Watch sale circulars and commercials the week of Christmas. This is when the stores will start announcing their after Christmas sales.
Decide to go to the "big box" stores that open early first, as you can hit smaller stores later. Crowds will increase around mid-day and last through the afternoon.
Shop online if possible and avoid the lines, parking and crowds. Get up early on December 26 to place your order; you won't be the only one doing this.