Distilled to their essence, what are the most important keys to improving your game? I see two: Good fundamentals and patience. Good fundamentals start with the stance, grip, positioning relative to the table, and footwork. They continue with using strokes you know are sound, struck no harder or more aggressively than you can handle consistently.
Patience is the willingness to stay in the point as long as it takes, and therefore to stay in the match until the last point is won.
Most long-time club players lack good fundamentals or are impatient to some degree. They rationalize these problems by focusing on quirky strengths (that one serve, or odd but sometimes effective individual shot), or a lack of available practice time. Some can go decades of weekly playing sessions never “having enough time” to correct the basics.
Good fundamentals and patience won’t necessarily make you a champion, but can allow anyone who is reasonably coordinated to become a decent player. Their absence condemns even the talented to a mediocre level at best. If you have played for a long time at the same level (especially sub 2000), chances are that you have deficiencies in these areas. It can be worth the effort and a little expense for a good coach to clue you in.