How to retain what you've read for longer durations

Last to last year, I picked up reading seriously and read a few books, but last year, I started my first job, so that habit broke.

I am again trying to get into the habit of reading. However, I am not able to recall anything that I have read in those books last to last year.

A little context: most of the books I read were self-help books and fiction, and at the time of reading them, I was really into them and understood most of what the writer was conveying, Or at least I thought I did, but 1-1.5 years later, I can't remember any of that.