Like all other collectibles, comic book values depend on the condition of the comic book, how popular the particular comic book was and how many of them are in circulation. The comic books that are not currently being published any more or back issues of a title are the ones that collector's want. The comic books that are most sought after are the earliest ones published in the 1930s and 40s, but any comic books published prior to 1961 are worth money depending on their condition.
The highest comic book values are paid for comics that are in mint condition. This means that they are almost the same as when they were purchased and only have small evidence of any wear and tear. If the comic book has a small tear or crease, the value does diminish, but not by a great deal. If, however, the book has a torn cover, missing pages and has writing on it, it is not if much value to a collector.
There are pricing books you can buy that will give you the comic book values for the titles that you have in your collection. There are also Internet sites such as Overstreet and Wizard that you can use to determine how much the comic books in your collection are worth.
If you have a comic book that is not one that collector's want, you should hold on to it because it may grow in value in the future. Checking which comic books are the top selling ones will give you an indication of which ones will be valuable in the future. The first issues are the comic books with the highest values. If you check around for comic book values, you will see that even with the most famous comic books, it is the first issues of each one that is worth the most money.