I store books in my library for my mother, my husband and myself. We all live together and anything slightly technical is my responsibility. I created a user column for each of us. Each column basically has 3 values - has the book been read by that individual, is it of any interest to that person Yes or No (all my romances are a NO for my husband for example). I also created a search criteria for each one of us. When I want to load books on my mother's reader I set the search to her name. This way I only see the books that she has not read but has an interest in. Each time I add a book I update this column for each of us. To keep it easy if the book is of interest and hasn't been read I just leave the column blank and fill it in with Read or Not Interested if appropriate.
I keep my tags for genre's. I find that the user column has worked really well for us for quite a few years. Both my husband and my mum keep a sticky note with their ereader and write down the book title and author when they start reading. Every so often I take their yellow sticky and update Calibre and delete the books from their ereaders and add a few new ones. It works for us.