The best way I've found is to go to an auction house. They have appraisers there that can help you to appraise the value of your antique items. If it is a piece of furniture, you can look for a number engraved on the backside, underside, or on one of the legs. They have several good antique websites online that can give you the value.
Any items value will be determined by the condition of the items. Some people feel books published in the 1930s are valuable. However, this isn't the case. Only books that are +100 years old will have a value to a collector and be worth something. This basically holds true for encyclopedias. Some other books will have a value, but the older the book the more valuable the book is to a collector is the books are in good condition.