Jewish homes have lots of books. Marie Kondo's suggestion of a 30-book limit just doesn't work for us. I think I keep that many on my bedside table (lol).
So when it comes to packing up bookcases prior to moving there's a lot of work to be done. I highly recommend doing a book purge prior to packing so you're only bringing books you love to your new home, but if you're ready to pack here are some tips. I highly recommend doing a book purge first and foremost, but presuming you are on the next step and ready to pack, here is what I suggest.
Color code by room
If you have more than one room with a bookcase and plan to have a similar setup in the new place, use colored stickers or colored duct tape to denote to which room the box belongs. For example living room=green, bedroom #1=blue, bedroom #2=yellow.
Label the side + top of the box. When the boxes are stacked, you can't see the labels
Separate kodesh (holy/religious) and chol (non-religious)
There is a halacha (Jewish law) about not stacking nonreligious books on top of a kodesh (holy) books which I confirmed this with my rabbi, so I would presume that what applies to stacking would also apply to packing. In practical lingo, keep your Gemorahs and Chumashim in separate boxes from your New York Times bestsellers.
Use small-sized boxes for books. If you are looking for second-hand boxes, ask around to see who has moved recently and offer to take the boxes off their hands. If you're hunting around town for boxes, the boxes that the 2-liter soda bottles come in are a nice size. Just don't use something too big or the box will get really heavy. Also, if possible, try to keep the boxes approximately the same size.
Pack by category
Think of a library and how books are arranged. They are grouped by topic. Some people already have similar topics grouped together. If you don't, no worries, and don't stress about it. Just consider organizing your shelves by categories post-move.
Securely re-enforce the tape at the bottom of the box
There's nothing worse than a poorly taped box that breaks open.
If you haven't started packing yet, I suggested doing a book purge. Here are my suggestions about how to downsize your book collection using what I call "the onion analogy" in How To Downsize Your Book Collection.
Questions about what to take/what not to take as you plan your aliyah, feel free to contact me.