Have a bookish url if you can. That way people know right away that you are a book blog.
Have a theme to one where your followers can see what you post and easier to navigate. It’s so cliche but the theme is one of the first things a potential follower will see and if they can’t figure the theme out (e.g. the next/prev page is missing or hard to see, the texts are too bright or small to read, etc) they won’t follow.
You can nicely ask other book blogs to check yours out and more often than not, they are very willing to help promote or even follow back. But don’t be rude and demand people to follow you.
Of course, following other book blogs makes them notice you more especially if you reblog from them. Interact with them, I know it can be intimidating - a simple “hi or what are you reading right now / what can you recommend to me” is a good conversation starter.
Know what you want to post. You can have quotes, gifs, pictures, graphics, or anything. It also lets your followers know what your interests are.
Share your favorite books. Ask for or give out recommendations
It helps a lot if you make your own too. It doesn’t need to be a spectacular graphic or elaborate gif, it can be a simple quote or pictures of your own books.
Be nice to your followers. Talk to your followers, it shows that you care and appreciate them.
Just keep posting and people will show up sooner or later once you get your momentum going. The first few months are the hardest.
Don’t pay too much attention to follower count and notes, what’s important is your happy with what you’re doing.