On the front of the bookmark students will write the title of the book they are reading along with the author of the book. On the back students will write new words that they come across.
It is suggested that you can laminate the bookmarks to use them repeatedly but I prefer for students to use a new bookmark for each book that they read. This way students have a record of all that they have read. If you have students keep a vocabulary journal you can have them transfer the words they collect on their vocabmarks to their journals.
If you would like more ideas for teaching vocabulary you can visit my vocabulary activities or vocabulary games pages.