Depends on the subject, I suppose. Each method/format has its advantages and disadvantages (except never learning, which isn't really an option)
Institutionalized learning (school) +Structure +Accountability +Guided learning -Not always an interesting format -Combination of structure and accountability takes away from the fun -Not much control over what you learn -Quality can vary depending on the institution -Potential cost
Practical learning while on the job +Usually practical knowledge, prioritizing the essentials +Getting paid to learn +Accountability (and possibly some structure) -Learning can feel stressful -Narrow scope of learning
Learning from your own mistakes +Experience can be a great teacher; more likely to ingrain certain lessons -Absurdly limited range of topics -If you're not sure why you actually made the mistake, can keep making it -Can completely miss certain things because you haven't encountered them; ie, some solutions won't occur you
Self-teaching through reading, documentaries, etc +Complete freedom, allowing you to study what you want and how much +Broadest range of topics and scope of learning -Almost entirely reliant on personal motivation -Lack of guidance and structure can greatly impede learning
Learning by conversing with others +Potentially wide array of subjects -Limited by who you know -You generally won't be talking to subject-matter experts so the information you receive may be of questionable quality or outright wrong. (Case-in-point would be learning about politics through Facebook.)
Learning through observing things such as nature or people +Watching others can help you detect your own blindspots +Original research -Impractical method -You won't necessarily learn best-practices
Other First thing to jump to mind is mentorship, which is a tremendous learning system (although limited by your mentor's or mentors' experiences)
Another is non-institutionalized structured learning like online courses and webinars.
I should make this post as subject to my.... Youtube video. Thanks zeus ---
You dont have to obey the white line, use the force