Solving Mathematical Problems: A personal perspective
Terence Tao
Deakin University Press, Geelong, Vic.: 1992
Hardcover. 85 pages. ISBN 0-7300-1365-0

This first edition is unfortunately completely out of print (the entire press no longer exists). It discusses various Olympiad level problems and how one can go about trying to solve them. Details on the second edition can be found here.

Here is the cover picture for the first edition, which was taken when I was sixteen:

sixteen.jpg

[Update, Jul 31: bad link fixed.]

[Update, Jan 24: fixed for real now, hopefully.]