If you appreciate art, investing in it can be a fun and profitable way to learn more about the subject and make some money as well. This is the kind of field where you really have to enjoy it to be any good at it. This is true of most things, but you can, for example, make money at trading items like pork bellies in the futures market without knowing or caring about the product at all. In the long run, you are always better off doing business in areas that interest you, but with art it's especially crucial. When you browse auction listings online, go to a live auction, or perhaps rummage through someone's basement during a house sale, you simply must have the "art bug" to maintain interest and gain any expertise.
There are, of course, many categories to choose from in art. There are many periods, locations, styles and media and you may have a very specific area of focus or take a more general approach. It is usually good to specialize at least to some degree or you will be overwhelmed by the myriad of objects to choose from. Personally, I have a liking for antique paintings, which is itself a very wide field. Antique can mean just about anything that is 19th Century or earlier (though some might include early 20th Century, depending on your definition of "antique"). There are also American, European, Asian and artists from every other corner of the world.
First of all, you may be wondering if art is a good investment. This is practically as impossible to answer as asking whether real estate or the stock market are good investments. In all these cases, the answer depends entirely on what, exactly, you are investing in. It also, alas, depends on market factors that cannot be predicted. With art, as with other investments, there are safer and more speculative choices. If you buy a well listed artist (one of your first investments, if you are at all serious, should be a reference book of artists and paintings, or perhaps an online subscription to a service with these listings), the value of your painting (I'm assuming you are buying paintings for the purpose of this article, but the same would be true of prints or sculptures) is almost certainly going to only rise, or, at worst, remain stable. With lesser known, or unknown artists you are always taking a bit of a risk. That's why one of the first rules of buying art is that, even if you are looking at it as an investment, only buy something you will enjoy owning, in case you end up in possession of it for a very long time!
There is another kind of risk involved when buying art. That is authenticity. There is, unfortunately, a great deal of ambiguity in the art world. There is also, even more sadly, a fair amount of outright fraud. As with autographs, not all signed paintings were actually signed by the artist whose name appears on them. There are many skilled forgers out there. There are also techniques to make works of art appear much older than they really are. Aside from outright fraud, there is also a vast gray area when it comes to selling art, especially at auctions, whether online or live. Many works, for example, are described "in the style of," "attributed to" or "...school." Sometimes these words have little or no meaning and are merely a silver-tongued auctioneer's way to make an unimportant work of art sound exciting. If you are spending small to modest sums of money -say anything from under $100 to a couple of thousand dollars on works of art, you have to face the fact that the rule is pretty much caveat emptor (let the buyer beware). If you are dealing with high-end auction houses, this kind of maneuver is less common, but by no means unknown. At least in these cases, you are more likely to be able to trace the provenance of the art. You will also have to spend more money, of course.
My own experience in the art world, I must confess, is at the lower end. I enjoy searching for unexpected treasures at yard sales, country auctions (though even these are now often attended by slick dealers) and second-hand stores. Naturally, if you are paying very little for your "investment." caution becomes less of an issue. The odds of finding anything worthwhile, especially today, when everyone is looking for a treasure to sell on Ebay, are rather depressing. Still, if you looking for good art investments, the rule is to keep your eyes open at all times.
Online auctions can be a fun and convenient way to shop for art. The dangers here are probably no more extreme than anywhere else, though you might think otherwise. People worry about the honesty of online dealers, fake bids (e.g. bids made by the seller using alternate IDs or by friends to jack up the price), but the same thing happens at live auctions. The rule is, be careful if you are spending any significant (to you) amount of money. This means, but is certainly not limited to, checking out the seller's feedback rating. Read any negative comments. Also, be sure to read the item's description very carefully. Some sellers are very skilled at misleading potential buyers without telling any outright lies. For example, some dealers sell antique *style* paintings in period frames (or period style frames). They may describe the painting, for example, as an English fox hunt scene, or a portrait of an 18th Century lady or gentleman. This does not mean that the painting itself comes from these periods. It could have been painted last month! Be sure to check the guarantee or refund policy of sellers. I've observed that most sellers who use the kind of tactics I've just described are also very explicit about offering no guarantees or refunds. Incidentally, most live auctions have similar stipulations if you read the find print when you buy something. Once again, caveat emptor!
I am certainly not trying to frighten potential investors in the art market, only point out some common tricks of the trade. If you are new to the field, start off small. Find an area that intrigues you and make small purchases. Do research in your specialty, or general area of interest. Read books and magazines that pertain to it. After making these relatively small purchases, see how quickly you can turn them over and if you make a profit. No matter how experienced you are, you will find that sometimes you will make mistakes and lose money. Other times you will break even or merely make or lose a few dollars. But you will also have those very rewarding windfalls that make it all worthwhile. It's best not to approach the art market expecting to make a killing, especially on any given purchase. That's how people end up overpaying and overbidding. Use your rational mind and intuition equally. Hopefully, over time, you will have acquired a skill and a bit of an education into the fascinating world of art!