I am seeing some online lectures and it seems so that my attention is decaying quite fast as time progresses in the lecture. Most lectures I find on the internet are 1hr yet the the time I can focus above 90% is like only 20 mins. So, often I end up chunking the lecture into small pieces. Another tip I found is to eliminate distractions and block out addictive social media sites before beginning the lecture.
What are some other tips I can keep in mind?
Take notes during the lecture. Preferably hand written notes as the better engage the brain in learning. After the lecture, write out a summary of the lecture capturing the, say, three most important points. Try to do this immediately.
I also suggest doing this on index cards. At least the summaries. One big idea per card. Use your own words. Number the cards sequentially.
Now you have a deck of cards from which you can select several to carry around with you for a few days for quick review while you need to wait for anything (bus, meal delivery, ...). You can also use the backs of the cards for notations of ideas you have as you travel about. Maybe add keywords to the cards as you think of things.
Finally, when you need to review for an exam or other use, the cards give you a way to recall the key points.
Orthogonal to the above is a suggestion that you put what you "learn" in any lecture to practice. If they provide exercises do them. If they don't then I question their overall merit. But you can compensate for that in many cases by finding a textbook on the same subject, perhaps one recommended, and do the exercises in that. Much harder, however, is to get feedback on your solutions. This is one of the biggest advantages of face-to-face education over online; personal individual feedback.
For (much) more on the idea of using note cards see the description of the Hipster PDA.
In general, you learn best by doing. Is the topic of the lecture amenable to a small coding project?
You learn by doing. Is there an associated set of homeworks?
You also learn by teaching. Make a presentation based on the lecture that summarizes it, mainly from memory.
I am afraid your question is too generic in order to give you concrete suggestions for improving your outcome.
Increase playback speed
If your attention span is shorter than the video, you could try shortening the video. Many video players have an option to increase the playback speed - an hour-long video played at 1.25x speed takes only 48 minutes. Your comprehension ability may suffer somewhat with increased speeds, but there is some evidence that losses can be mitigated by continuing to study with the saved time. Watching an hour-long video in 45 minutes at 1.33x and continuing to study for the remaining 15 minutes, or just watching the video twice in an hour at 2x speed, may yield similar retention results. Your ability to turn up the speed will depend on the subject matter and speaker, but it can be a good way to increase the "information density" of recorded lectures.
Here is a study examining the effects of playback speed on retention: Learning in Double Time.
