How Do You Buy Books?

I tend to buy books as they release, but it depends on how much money I have to spend. So, I've also got lists of books I want and use my wish list on Amazon to keep track of the ones I want to buy. If I haven't read the first books in the series, I usually put the rest of the books on my to-buy list. 

I love having the books waiting for me on my Kindle to read. When I'm looking for a book to read, I go through my Kindle library to find the one I want. 

How do you buy books? Do you buy them as they release or do you have a to-buy list?