Some Origami folds can be very useful. One of these is the triangle unit from which you can construct bookmarks.
Here are a couple of the ones I have made from this unit. If you glue two together you can make a Star of David. Using smaller units glued to larger units, you can make any number of patterns.
The triangle fold begins with a triangle. You fold the three points of the triangle to the top middle above. Next, you fold the top layer point down to the right corner and crease it. Do this on all three corners. Next, you lock these three tabs together like you would a cardboard box. Each of the three sides has a pocket which will slip over the corner of a book page to mark your spot.