"The mind of the beginner is empty, free of all habits of the expert, ready to accept, to doubt, and open to all the possibilites." Shunryu Suzuki, Zen master
Getting the most:
When we are looking to acquire new information, we start the selection process by refining the options, choosing one based on merit and then we begin learning. In defensive training, this means that we take a class to acquire skills or information we do not already have.
If we have gone as far as this step, we have acknowledged that we need this information, and that the source has the information that we lack. So, in preparation for the class, we need to ensure that we get as much out of it as possible. This means research into the techniques and training methods that the instructor uses. It means knowing what equipment the instructor requires you to bring and why. It means making sure that you have enough comfort items for the class that you do not end up falling out of the class and missing out because you forgot to take care of yourself.
If you have the ability, do some research into what the instructor teaches and why they teach that way. Overlay that skills and philosophy onto your own life and see how it matches with your experience and abilities.
If a class has a list of specific equipment, it is wise to pack everything on that list. Likely, that instructor has seen issues with other gear, has seen deficiencies with less gear, or simply wants you to be able to keep up with the class.
If you don't take care of yourself, you will be at a mental disadvantage. If you don't eat or drink water, your ability to absorb information decreases. Make sure you get enough sleep. Stay cool when it is warm and visa versa. If you are not at your best, information is lost in transfer.
And, most importantly, have an open mind. The information that you seek may not fit perfectly into your life, but some of the skills you take away can be invaluable. Pay attention. Get the most from your training.