Improvement in chess over years is usually related to the frequency of play and the addressing of discovered weaknesses as a result of your losses. One facet that I have discovered is that people tend to get stuck in a method of so-called 'training' and revert back to that method after a series of less-than-spectacular games played on their part. One tends to 'hunker down' and retrain using the same methods they used previously. The unfortunate thing is that those training methods, whatever they were, led to their current predicament, and are thus flawed in some way, were not executed properly, or did not meet the current needs of the player.
One way to address this phenomenon is to make available several
different training methodologies to yourself and rotate from one to
another. This enriches one's chess knowledge and makes available to the player differing perspectives from some of the great chess teachers throughout history. But what does that mean?
Here is a simple example regarding methods of thinking in chess and
how to select candidate moves. I am aware of several methodologies
regarding this process. I list them here:
1) How to Think Like a Grandmaster - Kotov Method
2) How to Choose A Chess Move - Andrew Soltis Method
3) How to Reassess Your Chess - Silman Method
4) B-Method: Squares Strategy - Bangiev Method
5) How to Become an Expert - Purdy Method
6) Chess Praxis - Nimzovich Method
7) Generic Chess Training System (GCTS) - Irina Mikhailova/Author's
Chess is an individual game. Because of that, training is almost
exclusively done on one's own. In regards to my own personal chess
training, I developed a hybrid system taken from Irina Mikhailova's
chess articles at Convekta, of CT-ART 3.0 fame. I have also studied
every method above at some point or another, beginning with Chess Praxis by Nimzovich in my chess youth, moving on to Kotov’s famous book, being overwhelmed there, moving on to Silman’s method, and currently engaged in the fourth method, Bangiev's Squares Strategy, which I find the most satisfying to date.
Chess is such a deep game that it requires each individual to become
creative, not only at the board, but also in their training methods,
to keep themselves fresh and their training relevant. This is why having available a rotation of differing methods of training is a must for the aspiring player. Solving tactical puzzles all day long will help you improve, sure, but it will not get you beyond a Category A level of play. True training is required to break that glass ceiling.