It's often said that you should write as often and as early as possible in your PhD, in part because practicing writing will make you a better writer.
This makes intuitive sense- after all, you can't improve without practicing- but not all practice is equally effective in improving your writing skill and simply engaging in the activity of writing on a frequent basis is not enough.
The learning curve and the plateau
If you started playing tennis every day, you would probably improve quite quickly in the first few weeks. But if you continued to play every day without adapting your training, your rate of improvement would slow to the point where you are no longer improving with practice.
The same is true of many skills. You can drive a car every day without becoming a better driver, you can go to the gym every day without becoming stronger and you can write every day without becoming a better writer.
The relationship between practice and skill is not linear. You may experience a rapid improvement early, but this improvement slows and your skill level reaches a plateau. This is known as the learning curve.

Sometimes your skill level can even decline with practice, so it's important to understand how to practice well.
Avoiding the plateau
To keep your skills improving, you need to adapt your practice. Usually, this means deliberately focusing on a specific aspect of the skill you are practicing and setting a clear objective.
A tennis player doesn't just practice tennis and hope they improve. Instead, they may spend an entire training session working on their serve, perhaps with the specific goal of improving accuracy by aiming for a small target on the court.
As a writer, you shouldn't just write and hope that your writing gets better. Instead, it's far better to focus on a specific aspect of your writing, such as;
- use of a specific tense
- clarity of expression
- rhythm and sentence structure
- structuring an argument
Good writing is a the result of many individual and complementary skills working in combination. If there is a weakness in your writing game, you have a far greater chance of improving if you make a conscious effort to focus on that weakness while you practice.
The crucial elements: feedback and adaptation
Two crucial elements of effective practice are feedback and adaptation. When you make an attempt at something, you need some kind of feedback to assess whether, or to what degree, you were successful.This means reading what you have just written and assessing your own work, and then adapting it to try to make it better. This isn't always easy to do- because assessing and adapting your writing is a skill in itself- but it's a vital part of the process. You can always get someone else to read a short section and give you feedback if you really struggle, you should try to assess your own writing first.
It is important that you do this on a small scale, reading and making small adjustments to short sections of work, rather than writing thousands and thousands of words. A single paragraph is enough to work with!
Take your time
It is difficult to improve skill under pressure or if you are working at speed. Slow down, take your time, and think.
Set aside some time, disconnected from the internet and other distractions, and be patient while you write. Try out different ways of phrasing things. Play with different ideas. Stop, assess, and adapt.
Practice alone isn't enough, and it can be deeply frustrating if you try your best and don't seem to be improving. If that's the case, more practice might not help, but changing the way you practice may be the answer.