There are several threads here, all of which I think are valid. As a former teacher, recognizing that everyone has his/her own learning style (auditory, visual, tactile, etc.), I doubt there is one "magic bullet" that kills every plateau.
If I had to pick one single factor, it would be to play over your own losses. We often hear advice to work on weaknesses, and any loss is due to a weakness or error so your own lost games are self-defining.
But study alone isn't worth much unless you can determine what the weakness really is. And that involves familiarity with openings, tactics, position and endgame skills.
So which comes first, the chicken or the egg? You build up chess "memory" and instinct by repetition which increases your speed in recognizing a weakness and decreases your analytical time. This is why better players can play a blitz game accurately, if not well. Repetition builds pattern recognition.
The whole thing comes full circle, and the better players are those who have the self-discipline to work on the things they don't like to work on. Put another way, successful players are those who are willing to do the things that lesser players are unwilling to do (assuming equal ability).
Isn't he rated 1039 USCF? Maybe I looked up the wrong person. I think you need to consistently solve tactical puzzles, try 20 a day or if it is better for you 20 minutes a day. I find that daily study of something helps me much more than intense study followed by near to no study for a period of time. Going over your losses was a great suggested several made too. The nice part about where we are at in playing strength is that we have a much easier time identifying and correcting our play and one little correction or improvement can go a long way in increasing our playing strength. Good luck in your improvements. :)