I tend to skip around a lot when I read, for example, skipping ahead, or reading the end of a book first, or every other chapter, or section, then jumping back to do the ones I missed on the first pass. It's not linear, but I can often end up reading most of a book that way.

If I must read from start to finish, it helps me to underline passages with a highlighter. This helps cement those in my brain and I get to break up the reading with using a pen.

I have also tried setting a timer for a certain amount of time, and forcing myself to read for that entire time. Then when the alarm goes off, I reward myself by allowing myself to get up and walk around or go put a load of laundry in the dryer or get a drink of water, etc. I find the timer really does help me. I tend to set it for 20 minutes at a time, but if that's too much, start with 10.