First of all get a reference book of some type. Either a Red Book by Yeoman, or a Blue Book also by Yeoman. (This is what I use, it's more like what you can get in real life unless you have a hard to find coin). Red Book is retail prices. Also can get retail prices from PCGS website. Depending on what your budget is, buy the semi keys. such as an 31s Lincoln or any of the low mintage Mercury dimes which can still be had at a reasonable price. Buy the best grade you can find and hold on to them. Even on Ebay I bid Blue Book price. I don't win many auctions, but occasionally I do. eg: 1908 $5 gold, AU (anacs) paid $135. 1819 AU 53 (anacs) Large cent $55. and others. Some bids get overlooked. I may win 1 out of 35 or 40 but doesn't hurt to bid. Finally get a book of grading coins. I find Photograde by Ruddy to be quite good. Stay away with lots saying unsearched. Even if they were, most coins prior to 1940 are already out of circulation.