I only have like 20 or 30 books that are unread on my shelf and that's not a lot. Most people have over 100 unread books and still buy new books, but they want to shrink their tbr's. How is it possible that I don't have a big tbr?
That's because I only buy books if I know if I'm going to read them in the next month or so and how many books I can read that month. Now I have vacation, which means I read more than when I have school. If I read 4 books in a month, I first read the books I have and if I finished them I buy more books.
So: read a few, and buy new ones if you finish those.
If you have 100+ unread books, then think: do I have to buy more books?! Or you can say to yourself how much money you can spend each month and more important: don't cross that rule! If you know you have 100+ unread books, then only buy I book that's a sequel to a book/series you've already read and buy 2 new books only if you've read 10 books you already have.
I hope this helps, because I really like to buy a book, read that one immediately and then buy a new book. So count your unread books and make rules!
How many unread books do you have and do you want to shrink yout tbr pile?