I typically re-read the LOTR, The Hobbit, and The Silmarillion once a year. Well, The Silmarillion is once every two years because, whew, it is a dense one.
Wow, that's a lot of rereading. Me and some friends do a LOTR watch party every year, making food and eating food as they eat it in the movies. But reading the books every year, that's quite a feat!