At the beginning of 2018 I declared Pocket bankruptcy and started fresh. Sadly I am again at 2000 unread articles and I am considering doing it again. I have the issue that I often add an entire backlog of articles, if I stumble upon a new interesting blog.
However in summer 2014 I started a habit that I had to go through 10 Pocket articles and 10 Evernote entries and read or delete it. For Evernote I checked whether the item had a long-term value for me and therefore I decided to either keep it or delete it. I also checked whether it was properly tagged and archived in my folder structure. 10 is a feasible amount and it will get you far over the course of a year-
The good thing is that you can basically do it anywhere, when waiting in line on the bus or even in bed 
I can see this being applied to long podcast backlogs, as well. Every day go through the list and decide upon 10 whether you actually want to hear it or delete it. As podcasts are comparably a larger time commitment than reading a short article, I would not include the actual hearing of the episode in that 10 items/day approach.
Somewhen last year I have set up Overcast to basically have an “inbox”. One smart playlist, where all new episodes show up in. I will regularly go through them and decide, which ones are worthwhile to listen to. Often times I will judge by the show notes or chapter marks and I selectively only listen to parts that are new. I will never listen to a podcast straight from the inbox, i always need to add it to my “priority” playlist, which is kept intentionally short.
For books the bookworm podcast actually motivated me to read more. My initial goal was to get to 20 books in 2020, which actually should be easy as 4 are already read.
For courses: I like tackling them one by one and spreading them out over time. Some of those “30 days of x” courses will come with a simple structure to implement. I tried putting the specific lecture/chapter in my calendar to have the commitment, but then it was a slow weekend I just plowed through a few chapters in one sitting and found that I would have to adjust all appointments in my calendar, which was too tedious.
This year I’m playing around with a one hour personal study session in the morning. It’s up to me what I do in it: go through a chapter of a course, read, draft, journal, meditate, draw/craft something small. It’s blocked out me-time. Just having that block of time so far works well.