Don’t rush into things…patience
Study as many systems as you can, a well rounded education can ensure that you learn many things instead of just sticking to one path or system.
Learn some meditations and techniques to develop your astral senses so you can effectively see and hear demons and enhance any abilities to intuitively or psychically connect with them. Good communication will ensure you can give the demons what they ask for in return and actually know what they are saying to you.
Don’t dismiss anything as stupid or fake until you have tried it for yourself. Not everything works the same for all magicians.
If a spell or evocation fails the first few times, keep trying, don’t give up!
Learn divination techniques such as tarot, runes, pendulum, etc. They will help you understand what’s going on if you do a spell and are unsure if it really worked. They can tell you if it did or not and if you need to repeat it or just wait it out. And they can also tell you if a particular spell or evocation will not end good for you and to avoid it.