"Seat Belt" Changes: - Making sure photos are all cropped/uploaded at the same resolution so collections look tidily aligned. - Taking product photos that are clean, simple, and well-lit... great product photos don't require a DSLR, just a bit of preparation, and the time to make them look good is worth it. - Setting up Google Analytics to start collecting data on visitors.
Airbag Changes: - SEO. Getting traffic is great, but if the site isn't compelling people to buy it's a wasted effort. - If you're not a capable designer, trying to make extensive changes to your site's layout can be extremely time-consuming and won't necessarily make your site look better. - Trying to round up hundreds of products for a brand new business. Keep things simple in the early stages and build out your product lines as you grow.
Those are just a few.