What makes a book collectable and valuable is their attributes. The following can all be attributes that affect the value of a book The Books Edition, Whether it is Signed, The Books Condition and if the book comes with any Extras.
Collectors, Dealers or Consumers are the main consumer groups and they sometimes look out for certain books in particluar. Certain authors are in HUGE demand, so it is always worth keeping an eye on their releases or if they are doing any signings near you. Here is my list of high demand authors Christopher Paolini, Philip Pullman, J.K. Rowling, Steve Augarde, Mark Haddon, Michelle Paver and Jacqueline Wilson.
If they are doing a signing in your area, buy as many as their books as you can, preferably try and get first editions and get them signed. If you cannot get your hands on a first edition, do not worry as sometimes their signature is worth so much you will make profit anyhow. You can tell whether your book is a first edition or not by the numberline on the copyright page. If the numberline has a number 1 in it, this is a first edition. i.e. 10 9 8 7 6 5 4 3 2 1 or 1 3 5 7 9 10 8 6 4 2
Getting extras like promotional material such as bookmarks, floor posters, cds etc is an added bonus. You can find them at book shops to try and obtain these. Bidders will love to bid on your lot if you are offering something out of the ordinary along with your book. If you can get these signed as well it is even better. These can be just as rare and valuable as some hard to find books. I hope I have covered mostly everything when investing into a book. To break it down into 5 steps 1. Try and buy your book in near mint condition as damaged books will fall in price. 2. Try and collect the first editions as they are the more desirable. 3. If you can pick up any promotional material along the way, do it. 4. Always keep your eyes open for desirable authors in your area as their signings could pick you up a few pounds. 5. Go with your instinct.
If you need anymore advice on which books or authors to go for, or if you want to know whether you have a book or something else that may have a value then you can contact me through my website.