Why People Buy
From what I've observed at art shows and online sales, the following seem to be the primary buying motivators (at least for women):
Pretty appeals to women. Now, it's true, beauty is in the eye of the behold, but we all know pretty when we see it. What makes something pretty? Whether it's a face, a room, a painting, a car, etc., the "elements of design" of the object observed is pretty if it obeys most, if not all, of the "principles of design". I'll do a post on these "elements and principles" next. Bottom line: Pretty sells.
People buy color. Some colors are more popular than others. Some color combinations are currently in style while some colors never go out of style. Blue has always been the most universally popular color. Pink and gray combination was popular a little while ago. Gray is still hot, but turquoise and mustard seem to be having a moment
Study current trends, recent past trends, and popular colors when choosing your color palette. I know, this is cravenly commercial. But, come on, everybody just wants to sell, right?
If you're going to a show, have as many color choices as you can to increase sales. Some people specialize in one color palette and there's merit in that. In this case, make sure the show you're going to has a BIG attendance. Otherwise, I think it's best to have a variety of colors, with special emphasis on current tends. And lots of blue.
Subject Matter of Your Art
Know someone who collects owls? They can't pass one up. Live on the beach? Beachy scenes, critters, and objects are your decorating choices. People are drawn to certain themes, objects, or animals and they buy them (if they're pretty and the right color. See above.) Studying online shopping sites and catalogues will give you lots of clues as to what people are buying. For easy sales, paint stuff people are collecting.
Art That Touches The Heart
Whether people are collecting or not, if your art touches their heart, they can't resist it. Animals, children, and certain scenes pull at the heart strings and is something they'll want to take it home with them or give as a gift. Paint what people love or in such a way as to make them love it.
There you have it. My little take on making what sells. Now, go make some art.