The basics of MTB riding involve bike setup, confidence, stability, and riding to improve your current skill level.
Firstly, before anything, you need to ensure that your bike is set-up properly to suit your riding position. Your riding position is usually based on your height, reach, and type of cycling you do.
Secondly, confidence. Don’t doubt yourself but neither should you ride too far above your skill level trying to “impress” surrounding riders. This is false confidence and is the first step to the destruction of confidence.
Lastly, getting out of your comfort zone, try new things. Riding to a small level above your current skill, makes your mind, muscle memory, and confidence adapt to new obstacles and skills.