I want to make a quality photo book. Some of my family photos from many years ago are too blury to enlarge very much and still look good. Some of them show definite signs of jpg artifacts beyond a certain enlargement. My computer screen is using about 72dpi. I want to create pdfs at 300dpi for the book. What's the relationship between what looks good on my monitor and what will also look good on the book?

thanks for any help.