These two books are worth their weight in gold (though being books, they're really not all that heavy):
Green Eyes, Black Rifles by Kyle Lamb
M16/M4 Handbook by Mike Pannone
In addition, take a course from a reputable instructor. You can only learn so much from the books alone.
Where there is discord, may we bring harmony. Where there is error, may we bring truth. And where there is dispair, may be bring hope.