1st Printing: The first printing is highly sought after by collectors and thus more valuable.
The first printing has the Gygax/Kaye logo and has the word 'Additional' set in wide letters. (see picture above).
2nd Printing: The second printing (July 1975) has the Gygax/Kaye logo and has the word 'Additional' set in narrow letters.
Image courtesy of Kynan Connor, USA.
3rd to 7th Printing: These printings have the TSR lizardman logo on the cover. The printing information is given on the first page of the booklet.
8th to 12th Printing: These printings have the TSR wizard logo on the cover. The printing information is given on the first page of the booklet.