You will need:
Paper
Scissors
A pencil, pen, or crayons
Something to bind your book together like string or staples. 

Cut your paper into coupon size pieces.  Bind the papers together into a book with either staples or punch a hole at the corner and put a string or yarn through the hole and tie it in a knot.

Make your coupons.  The coupons can say anything you wish.  Some popular coupons are:
Redeem this coupon for one big hug.
Redeem this coupon and I will clean my room
Redeem this coupon for one free car wash
Redeen this coupon for breakfast in bed 
Redeen this coupon for a kiss
Redeem this coupon for sweeping out the garage

You can make up as many coupons as you wish.  These make a nice gift.

If you are making a LOVE Coupon book or a Valentine Coupon book you could print this heart to place your writing in and bind the hearts into a book.