How to Make Page Corners

Lame bookmarks? Try this!
Square Paper

Fold the paper diagonally in half as shown in the picture.
The "Corner"

Take the left tip and fold it up to the upper center corner. Do it on the next side. Unfold. These are the flaps.
The Pocket

Using the uppermost layer, fold it to the bottom center (where the creases of the previous folds meet). This will serve as the pocket for the flaps.
Going "IN"

Fold the "flaps" like what you did to it a while ago.
"IN" Process

Fold the flaps into the "pockets", creasing sharply. The tip of the flaps should be in the middle inside so it would fit on the page.
"IN" Process Finished

This is the product of step 5.
Decorating Time!

The most fun part: DECORATING! The decoration you want to see should be placed on the flaps. The other parts won't be visible in use.
Use Your Work of Art!

Insert the corner of the page in the pocket (the same place where you placed the flaps). TA-DAHHHH! Your new bookmark.