What you can see for yourself.
The most useful thing is not to put a name to what you see, but to date it. A photograph taken from the front, smiling with your teeth showing, in daylight, is worth more than a description; if you come across an old photo, keep both.
Also note when any discomfort occurs, with cold or when chewing, and how long it has been happening. These notes will save you from having to reconstruct from memory, on the day, what you had noticed.
Is it urgent?
Tooth wear often develops gradually. How soon you need to be seen depends mainly on any associated signs and on how quickly the change appeared.
Some signs, however, are a reason not to wait: severe or persistent pain, a tooth or an edge that fractures, or a change that has appeared quickly. In these situations, it is better to seek advice promptly rather than put off the appointment.
What to avoid in the meantime.
The actions that make things worse are almost always the ones added in the belief that they will help.
Brushing harder, or switching to a harder toothbrush, does not clean a worn surface any better. Nor is this the time to start whitening your teeth on your own, or to start using a product sold as “polishing”.
These are precautions, not a treatment: your usual oral hygiene does not need to change in the meantime.
What the first appointment can establish.
Expect to talk as much as to open your mouth: what you eat, how you sleep and any medication you take guide the examination as much as what can be seen.
This appointment establishes a starting point; it does not decide on a treatment. Leaving with no treatment planned is not the same as leaving without an answer: it is often the conclusion of an examination that has done its job.
What happens next depends on what has been found. In the meantime, understanding the mechanisms of tooth wear helps you know what will be discussed.