As an artist, I have an idea of what is working for myself and others. Exposure is important, and something is better than nothing- but certain ways are better than others.
1) Vanity Galleries- galleries where you pay for spots on the wall- are almost never a good idea. Their money is coming from the artists, so there is no practical motivation for them to sell your work. However, if you already have a solid customer base, and you believe your customers would be likely to visit in order to buy (as opposed to, say, visiting you at your home), then it could be worth doing.
2) Traditional Galleries- notoriously difficult to get into, it can be a discouraging process, but rewarding, under the right circumstances. Brace yourself for rejection, and create a cohesive portfolio- a definite style. Be ready to offer yourself in pictures, slides, and professional looking, framed (if they're two dimensional) pieces. Be polite, but insistent. Do not approach the gallery owner while they are obviously busy, especially if they are trying to make a sale. When you do approach, do it in person, with materials, asking for an appointment- it is more difficult to refuse a real, live person in person or over the phone than through the mail. If you come to an agreement, then there should be a contract written up, and you should review it carefully. Also, do not jump in the deep end with a gallery that you cannot visit regularly- you have to remember that not all of them will be reputable. If you believe your clients will support the 40-60% commission that a gallery will request, then it can be a wonderful, hands-free methods of selling your artwork.
3) Art galleries/ Frames shops- Personally, I have never seen this one work, but I am sure it could. Set up in a style that works with the rest of the store, and understand that- if their income is mostly coming from the frames, not the works- your pieces will be used more as a look-how-nice-we-can-make-your-stuff-look examples than anything else. Put your contact information on a small but visible tag next to your work, as well as a price if they will allow it, and try to make sure that the contract is open-ended, since you don't want your work tied up forever somewhere if it does not make you any sales.
4) Alternate Venues- these are places like cafes, restaurants, libraries, bookstores, art supply stores, that sort of thing. Often they ask for little to no commission, and you can put tags and contact information on the pieces themselves. If you select the locale carefully, make sure the clientele is the sort that will support you, then it can be a fairly profitable venture. If it is the wrong place, then it is quite possible that you are decorating the location for free.
5) Slightly-Less-Alternate Venues- garden centers, furniture sales stores, paint stores, places that sell flooring, tile, drapes- anywhere that sets up their wares in a faux room arrangement, and wants to sell them. They will generally ask for much lower prices- and commissions- than galleries, and don't know as much about selling fine artwork, but pieces can move more quickly than you might expect. It is not top-of-the-line, but it can be a very good step.
6) Fairs- They require a lot of set up, transporting your work from one place to another, talking to the customers, having to sell your own work. If you're naturally gregarious, that is wonderful. If your work is naturally salable, the sort of thing that welcomes public consumption, then they can be a wonderful choice. You spend time with other artists, get a feel for how others will react to your work, and often do quite well financially. Downside- you have to pay for the space, buy things like tents and tables, and it is a bit of a gamble. Make your area welcoming, friendly, at one with your style. And, if at all possible, do demonstrations in your booth. It will attract interest, and give you something to talk with your potential clients about.
7) Other Indoor or Outdoor Fairs- Such as wine tastings and that sort of thing, not art focused, but could be ideal if it draws the right crowd for you. Check on the background- this is a newish field, and you should check with artists that have participated in them in the past.
8) House Parties- think something like a tupperware party. Borrow a friend's nice house for a small party, promising them a percentage of sales. Invite your friends, especially the ones with money and your kind of taste- hate to sound cynical here- and have the friend invite theirs. Provide alcohol and snacks, perhaps be ready to play some minor games, and definitely be ready to provide detailed, even emotional information about your work. It may sound hokey, but this is something I have seen work very well, and it is the best way I have found to get and keep loyal collectors.
9) Online Opportunities- there are a lot of these around. I personally do not know any artists with their own website. I believe this would be a viable sales venue, but it is expensive to have a quality one set up. Pay-to-displays are much along the same lines as the Vanity Galleries. On the other hand, websites such as webshots.com, deviantart.com, facebook.com, and myspace.com are simple, easy ways to keep everyone up-to-the-minute on your artwork, with fun and personal touches. You are unlikely to make any direct sales from this method, but it can provide and strengthen the contacts necessary for a really strong career in art.
In general, make sure that your work is at a level and location where it is best viewed (usually eye level, approx. 6 feet away), that it is clearly marked as yours (a small card on the wall next to it), and do not overwhelm your potential buyers with too many options. Frames can make all the difference in the world, if it is appropriate for your work, and people always, always, always are more willing to buy if they can just take it home and hang it rather than trying to get it framed or wired themselves.
Other things to remember- holidays are big. They are a splurge period, and some people will buy artwork for others as gifts. Also remember that season-appropriate work is more likely to sell.
I hope this helps! I know that it is possible to make money with your artwork, and I wish you all the best of luck!