Thankyou for the comments and the half hour video.
This is what I understood from the above video ...
Dr. Hack Chess problem solving system: For 1400 -1700
1. Who can be checked?
2. What is left hanging?
3. How to exchange a piece: Smaller valued pieces attack bigger valued ones.
4. Is there something better ?
------------------------------------------------------------------------------
Besides the system, what I noticed in the above video puzzles was ...
Pieces that line-up (in a row, diagonal, column or aim in a common sector) can cause tactical problems.
-------------------------------------------------------------------------------
Thank you for the video and looking forward to Watch (more) Stream Puzzles.
I guess the above video could be added to a link like this:
lichess.org/video?tags=solving/tacticsBut ... I think videos that use Lichess site puzzles, should be sorted in a better separate section. It would be useful if the videos that coaches used to explain things from this site be sorted like Lichess TV or Lichess Library, but saying : Watch» Lichess Puzzles.