Drawabox: A skill-improving resource that focuses on structured “exercises that train muscle memory and develop concrete skills in a way that appeal to an analytical mind. The lessons here won’t turn you into a master on their own – they will however set you on the right path, help you develop the confidence you need to move forwards, and will leave you with a solid foundation that will be critical in further development of your skills. Whether you’re a beginner or self-taught – all you need to bring to the table is the patience and conscientiousness to follow the instructions as they are written and demonstrated, and a willingness to accept and appreciate all your mistakes and failures along the way.”
The Sequential Arts Workshop: SAW, founded by cartoonists Tom Hart and Leela Corman, is a school in Florida and online, and while taking classes (rightly) involves money, they do have a nice pile of free online resources. (Creating an account is required.)