If I had to give only one piece of advice to a young student, it would be to do everything possible to avoid injuries.
When we are young, the body heals quicker. So getting injured is not necessarily a big deal. Also, there is a certain bravado in handling an injury. But some injuries such as torn ligaments, broken bones, etc. can become serious impediments later in life.
I know from experience as I now deal with the effects of a serious knee injury from 1994. I injured it again in 2008 and now have to be very careful with certain movements. In other words, I am less free in my abilities.
When you get older, mobility is freedom. If it is compromised, you will lament those old injuries, so do what you can when young to avoid them.
Wear safety equipment and follow protocols for careful partner practice. This is some of the equipment that will help prevent injuries.
(no link for these as I am not selling equipment)
The bottom line is awareness.
Each exercise, form, application set up, etc. is unique so one needs to consider the most important question, “what can go wrong?” The answer to this will clarify things like the speed at which to practice, how intense the contact should be, signals to end an application, whether it should be monitored by an observer.
Martial arts is obviously about self-defense and personal development. This starts with care and concern for fellow students while ensuring one is able to practice safely.
Surely, it should be obvious that getting a serious injury while training is the antithesis of self-defense.