I've had this problem sometimes, I find it can be a combination of a) I can't get into the habit and b) the book itself is boring. Sometimes I find I need to actively set aside time to read, which can sometimes include forcing myself to sit down and do it. Once I get into it, it's easy to keep going, but you need the time to get into the book in the first place! And of course to do that, you need a book you enjoy. It's no good forcing yourself to read a book you don't enjoy, that'll just make things worse.
One thing that helps me is to remind myself that I can read any time. So if I find myself sitting around at home, wasting time looking at addictive social media or youtube videos, it's time to pull away and maybe get out a book instead. I also take a book whenever I go to the doctor's since there will inevitably be waiting times and that's a good way to pass them by. One thing I have found is the more I read the more I want to read, so after initially pushing myself to get started (or re-started) after a long period of not reading, I get into it, and I don't need to push myself to do it any more.
If you have a kindle or reading app, downloading the free samples of books can also help, so you don't end up buying something you don't like, and then feeling like you HAVE to read it just 'cause you bought it. (Sounds obvious, but I wasted loads of time/money before I realised I could do this!)