The main problem in learning a new skill is maintaining the required motivation and discipline, especially in the early stages.  Gamification deals with this problem better than any of the other approaches I’m familiar with.  Over the past few months, I’ve managed to study maths, languages, coding, Chinese characters, and more on a daily basis, with barely any interruptions.  I accomplished this by simply taking advantage of the many gamified learning resources available online for free.  Here are the sites I have tried and can recommend:

• Codecademy. For learning computer languages (Ruby, Python, PHP, and others).
• Duolingo. For learning the major Indo-European languages (English, German, French, Italian, Portuguese and Spanish).
• Khan Academy. For learning maths. They also teach several other disciplines, but they offer mostly videos with only a few exercises.
• Memrise. For memorizing stuff, especially vocabulary.  The courses vary in quality; the ones on Mandarin Chinese are excellent.
• Vocabulary.com.  For memorizing English vocabulary.

Am I missing anything? Please leave your suggestions in the comments section. Thanks!