37 Signals has a list of holiday "to-do's" on your e-commerce website to prepare it for the holiday shopping season. Since Christmas often accounts for up to 40% of a store's entire yearly profits, there's no doubt as to the importance of prepping your site for holiday shoppers, even in July.

Remember that since many webdev projects will take you 3-4 months to complete and another to test, July may be too late, rather than too soon to begin preparations. In addition, links and content built now may take considerable time to be indexed and ranked well at the major SEs, so planning ahead becomes important for traffic purposes, too.

At the Holiday E-Commerce Ideas list, they've got suggestions ranging form logo design to gift cards to shipping to re-organization of information architecture. It's worth a read if you want to be ahead of the game on Black Friday.