Teach. If you're an expert in a certain subject, see if the community, local colleges, or even the private high schools in your area are looking for a teacher in your field. If you can pick up just one night class per week, it can make a difference in your income. Though you'll need certification to be a traditional teacher most of the time, to teach part-time you may only need a master's degree and proof of your expertise.
Jack up your prices. If you're providing a skill, service or product that is in high demand and low supply, and you're making the most of your time, you should be making good money. Unfortunately, there are many people who are too humble or fearful to demand that they get paid accordingly. It's the pushovers in life who get taken advantage of and exploited, so if you think you might be one of them, learn how to stop being a people pleaser. If you work for someone else, ask for a pay raise or get a promotion, and if none of that pans out, revisit your career options as described previously. If you're self-employed, the first thing to do is to make sure your customers and clients pay up on time--this alone can substantially improve your income. Check your prices and rates against those of your competitors--are you undercutting them? Why? If you're providing a superior product or service, you should be getting at least the average, unless your profitability depends on mass production, in which case you're probably making a lot of money and wouldn't be reading this article anyway!
Websites like Survey Junkie will pay you a decent chunk of change for the low-maintenance, borderline mindless task of completing surveys. Companies want to understand consumers better, and one way they do that is by compensating survey-takers. Most surveys pay between $0.50 and $1.25, and many of them take less than 5 minutes to do. You can read our full Survey Junkie review for more info.