I'm usually fairly consistent, but sometimes I have to go to league matches directly from a busy day at work. Mentally I can be a bit sluggish in my first match on those nights, playing on autopilot and not paying as much attention to my opponent.
I tend to improve slowly over time as I play, but a lot faster with coaching. My form sometimes dips for a while when I'm trying to learn and implement a certain strategy or shot for a specific situation. I think it's why coaching is a bit of an all or nothing thing. If you're going to do it, you should either just do 1-2 sessions and pick up general ideas, or you should commit for a good 3-4 months and really work on implementing a specific skill or strategy.
Coach quality and philosophy matters too. A lot of coaches don't work with the player, and instead they focus too hard on building what they believe is the "ideal" player. I think this works really well for juniors and for people with a lot of time for both coaching and playing.
For people already having played for a while (and therefore ingraining certain habits and techniques, for better or worse) or with limited time, I believe the best coaches assess the player's unique sort of 'template' and focus on building the skills the player needs to use their strengths to their fullest, building a solid serve and receive game that suits them, and reducing unforced errors.
