There are a lot of methods here. I’ve used the wordpress method but with that you get EVERYTHING with not much control. The one that gives me the most control (and imo the best) is tumblr-utils by bbolli on github. It can be daunting for those who aren’t familiar with command line, however. They do have a Windows guide (tumblr_backup_for_beginners) which walks you through step by step on setting it up and getting it started.
Below is my version of the guide with some helpful tips not mentioned, under read more for length.
One more reblog. Because it breaks down the steps a little easier.
Mspoodle 