I have about four book of shadows so far, each of them completely filled, so to condense all the knowledge in them I bought a 5 inch 3 ring binder, binder paper, dividers, highlighters, scissors, glue, and tape. I went through all my bos's and copied the information I found helpful, then I went through all the magick books I have aquired over the years, looked through them, found the pages I found the most helpful, ripped them out, and glued them on to paper I put in my binder. I found this to be quite helpful, and thought I would share it with you guys.
My own BOS just started a few months ago. A friend of mine (who just started practicing) wanted to collect spells and information and wanted me to help her add to it. I figured after a few years of practice it was a good idea to set up a binder of things I found helpful or useful over all this time and combine this into the same book.
My first BoS was started in a Trapper Keeper back in 1987. I still have many of my old spells, rituals, ect.. from that first BoS. I use a big 3 ring binder too. Plastic page slips are wonderful. I use tagboard to separate the sections. I try to keep my main BoS looking nice, so I have transferred parts of it to smaller binders.
I've actually just handmade my main book of shadows. It's got like 1,000 pages an I'm kinda hoping it will become an old family heirloom. At least, that's the idea. I tend to get reall fanc with my books to. Ill often full on illuminate the pages and design all the pages.