There are a few books on icons that are worth reading.
However not all of them are still in print!
The books below are available from Amazon however, (click on the cover
picture or name for more details):
Theology of the Icon, Leonid Ouspensky, 1992
The Russian Icon: From its Origin to the 16th Century, Viktor Nikitic
The Icon: Window on the Kingdom, Michel Quenot, 1992
The Meaning of Icons, Leonid Ouspensky, Vladimir Lossky, 1983
Sacred Doorways: A Beginner's Guide to Icons, Linette Martin, 2002