There are many free online courses that you can take to boost your skills and make yourself more marketable as an online worker. You can try sites like Coursera, edX, and Udemy to learn to program or acquire advanced skills in Excel. You can also try YouTube because it probably has a video on almost any topic. During lulls in my work, I usually watch videos uploaded by other freelancers in order to discover new earning sites. Some channels offer reviews or tips for working on these sites.