It's an artist's dream - to work from home, creating the artwork they enjoy, and making enough money to do whatever it is they want to do. For every artist that achieves their dream, there are thousands who struggle along trying to make ends meet. There's a reason that the stereotype of "poor, struggling artist" exists :) Take heart, though - it is certainly possible.
First, it's important to realize that you need to work on your skills. If you only half-heartedly try painting once every year, you can't expect people to reward your lack of effort. Typically the artists who do well pour a huge amount of time into perfecting their skills. They read books on their style of painting or drawing. They get feedback from friends and family. They go to art museums and learn about other techniques. They take courses at local colleges. Yes, you want your art style to be your own. But you want to be as good as you can at what you do.
Next, build up your network of visibility. If your paintings are the best the world has ever seen - but they are all down in your basement and not seen by anybody - how can people appreciate them? Build a website highlighting all of your best works. Enter your items in fairs and festivals. Volunteer to donate an item at your local town's event or an event on the theme of your painting.
Remember, a painting is a luxury item. Nobody "needs" a painting. Also, a painting is a permanent object. If you buy a soap and don't really like it, it is gone in a week or two anyway. If you buy a painting, that is a far more long term issue. You have to really connect, emotionally, with the buyer in order for them to want to see this item every day of their life.
Part of the key here is to choose themes that people enjoy. I'm not saying to custom create your artwork to be "popular". But I'm saying to look at what you like to paint about, and see which topics might be ones that are easy for people to love - at least to get you started. Let's say you like dragons. There are a TON of people out there who love dragons! If you did 10 different paintings of dragons, and showed them at science fiction / fantasy conventions around the US, you could build up an incredibly loyal following. At that point you could paint just about anything else you wanted, and those dragon-lovers would help to publicize you.
Painting on a theme also helps you in the multiple-purchase area. If someone loves your artwork, they are likely to be interested in getting multiple pieces over time. If you did a series on lighthouses, a lighthouse fanatic might want several of your works, one for each room. It's always easier to sell to someone who already appreciates you, vs having to start from scratch with a potential new buyer
Popular Themes for Drawing / Painting
It's important to note here that I'm not saying to only use your artistic talent for "popular causes". However if you are naturally interested in one of these topics, it could give you a VERY easy stream of money and a loyal fan following. Once you have those established, you can then branch out and expose people to other ideas. It's like with anything in life. You need to get someone interested in the basics first before you can then help to gently expand their horizons.
Lighthouses People love the imagery of lighthouses - they keep people safe, they bring you home, they take you from the rough seas to the calm land. It's very emotional and soothing. General seascapes are also popular.
Dragons / Fairies There is a very large segment of new age people, and the popularity of Harry Potter and Lord of the Rings has helped it along. This is great for the imaginative artist, because you can draw these items in just about any way imagineable and find an audience for your vision. There are tons of sci-fi festivals at which to show your work.
Animal Type Just about every person has a favorite animal. Some popular ones are cat breeds, dog breeds, horses, dolphins, wolves, lions, tigers. There are people who decorate their entire home along such a theme. If you created a webpage full of tiger artwork, for example, you probably would never have to advertise. All the tiger lovers in the world would find you and ask for your items. The more specific you get, the better you will do as the "only artist in this niche". If you did Arabian Horses for example, you would find a quite loyal following.
Bird Types I include birds separately because most people have a favorite animal AND a favorite bird. Popular birds include eagles, hummingbirds, robins, and bluebirds. Flower Type Most people have a favorite flower that has great meaning to them. Popular items include the rose, lily, daisy, sunflower, violet. Roses are especially popular and romantic.
Hobby / Sport Traditional hobbies involve people who love to be reminded of their hobbies. Paintings of fishing, hunting, quilting, knitting, biking, golfing, camping, tennis, football, baseball, etc. are always popular with those groups
Portraits of People, Animals, Homes
Where people might pay X dollars for a painting of a generic dog, they might easily pay 10 x X dollars for a painting of THEIR dog. You don't even have to do the painting based on the real live dog. If you ask them for 3 or 4 photos of the dog, it can do just as nicely for a basis.
People love having paintings and drawings of themselves, their kids, their pets, their homes, their cars and boats. It traces back to the idea of old English manors having huge paintings of the family members. It was a luxury that only the most wealthy could afford. In modern days, many more people have spare money that they can use for these reasons. When they commission a painting of something they really love, it seems far less like a frivolous activity. It seems more like a lifetime purchase that they will truly enjoy and treasure.
Of course the trick is that the painting needs to be flattering. If the commission is for a painting of husband and wife in love, and you make them look like hideous monsters from the deep, don't expect your buyers to be thrilled!