Rare books can be of great value, especially if they are first edition and in good condition. It is absolutely imperative that you keep your books in the best possible condition if you want them to retain their current worth and increase in value. The condition of the dustjacket is of vital importance in determining the value of the book. If you have old rare books or indeed new first editions which you wish to keep as investments, you should buy mylar covers to protect them. Many first edition books which are worth very sizable amounts of money with good well preserved dust jackets, are worth only a fraction of that value, if the dust jacket is badly damaged or misssing. Another vital factor in helping you determine the value of a book is to check that the book is not price clipped, again many potentially valuable books may be quite worthless if they have been price clipped.
If the book has the name of the previous owner or other writing on it, this too can considerably lessen its value.If you possess a few new first editions, resist the temptation to scrawl your name all over the inside cover, after all you know who owns them.
There are a number of good websites where you can get a reasonable estimate of the value of your books, you can check what other copies of your books are fetching on Abebooks.com and on bookfinder.com to name just two of the better known sites. It is also worth checking on e-bay to see if your books are for sale there, and what sort of prices they are selling for.
if you wish to start a collection of books that you hope will appreciate in value over time, then a good starting point is to buy first editions of prize winning books, there will always be collectors of the Booker and Pulitzer prize winning titles. The same is true of biographies of famous people particularly leading politicians, again you cannot go wrong with American Presidents or British Prime Ministers. If your first editions are signed by the author then their value is obviously considerably increased. Beware of collecting very popular writers as they may not stand the test of time, and both the author and the books could be completely forgotten in a few years.
Book collecting is an interesting and profitable hobby,and believe me it is quite a thrill, when you pick up a bargain signed first edition in the local charity shop or second hand book shop, at a price maybe hundreds of times less than its real value.