Unfortunately, there is no direct method or feature to allow you to upload or create pre-draft rankings. This is something we hope to build in the future, though.
However, as a workaround, users can pre-set queues within individual draft rooms. To set a queue within a specific league, make sure the league has a pending draft with a draft order setup and date/time scheduled.
Once on this page, you'll be able to scroll through the list of available players and add them to your queue. This queue will carry over and can be updated before and during your draft.