Mae- there are no rules. Some people use thinner paper at the back and also mount pics on cardstock and paper, or the other way around, prob depends how you want it to look. I do not use glue on my pictures at all, I glue paper to paper or cardstock, but I use double sided tape on my photos as they are easier to remove if I wanted to, and glue smears and dripping worries me. So you can use tape that you cut or squares that are pre cut, or even those tape runners or dispensers. But rules....NONE! Take a look in some Magaines for ideas etc.