It's tougher than it looks. You'll have to market yourself if your doing fiction, or the info product if that's your model -- extensively. It really only becomes passive income once people start looking for your work, rather than stumbling on it like they will at the start.
If you have lots of traffic streams and online marketing expertise you'll likely have an easier time than I did, but thinking that you're going to capitalize on this Christmas' boom is very unrealistic -- not impossible since I know nothing about you -- but it's not a set-and-forget deal by any means. You need a lot of sales because even great authors sell their books at 2.99 or slightly higher, which means you have to sell LOTS to make significant money. Also you really can't stop at one book because you want to create a snowball effect to really drive up sales and break the top-100 in their ranking system.
Read... extensively and check out the amazon forum and guys like
JA Konrath who're successful. There are tons of terrible authors making money, but they don't do it passively.