Open your book to its copyright page. Depending on whether your book contains a blank page at the beginning, the copyright page will be its first or second left-facing page.
Inspect the page for a sequence of numbers without any special characters, such as "10 9 8 7 6 5 4 3 2 1," for example. If the last number in your sequence is "1," you can be sure your book is first edition.
Locate a second string of numbers in the format "0/4 05 06 07 08," as well as the date of publication for the book's first edition, which will be located nearby. If the text tells you the book was first printed in February 2004 and the first number in this sequence is "0/4," this confirms that your book is first edition. If, on the other hand, the year of the first edition doesn't match the first number of this sequence, you book is not a first edition.