Practice. I've had a couple periods where I went from reading constantly to not reading at all, and the only way to read more in one sitting is to read more. At the start you may only be able to do 15 minutes or so before you have to get back to the feed, and that's ok. Later that day you can do another 15 minutes, and tomorrow you can bump that to 30 minutes at a time. You can jump-start that by reading things that keep you glued to your seat rather than things that you need to read, like fiction instead of, say, an O'Reilly manual, but those books that are in the "want to have read" category instead of the "want to read" group are always going to be harder