First of all, people include parents, teachers and other people who come into contact with them. This is a recognized teacher.

The second thing is what you have experienced or seen/heard, as long as you are diligent in thinking.

Everyone can help you and become your teacher.

Third, the life around them, whether animals or plants, actually has its own survival skills.

As long as you can observe carefully, you can learn a lot from it.

Fourth, contact with the surrounding objects is actually the crystallization of the wisdom of countless predecessors.

If you have more time, it is extraordinary to observe everything around you carefully.

You can appreciate many things that you wouldn't normally notice.

In short, everything around you can be your own teacher.

However, in my personal opinion, you can only refer to the first two. If you have a lot of time, you can consider the last two.