Hello Vex,
I would suggest, that you make yourself familiar with the Meditation of the Inner Temple, as this is the method taught to students of our mystery school. If you are taking the free online qabbalah course, you will work with the Inner Temple more intensly after you successfully complete the first course month. If you opt for a membership, you will even have the chance to get a personal mentor who assists you with your personal progress (correspondence course).
As you ask for trusted sources: The course book "An Introduction fo Magic and Meditation" by Salomo Baal-Shem is a valuable resource, although it is not a necessity for the course or the meditation. You will find every essential resscource online on this website, or on the qabbalah.de website. If you are not explicitly looking for external sources, I would rather refrain from recommending them at this stage. That is because I believe it is best that you use the same framework as everyone here, which is the Meditation of the Inner Temple - that way we have a common ground for our experiences and discussions. Plus, I do honestly believe in its quality.
Hope I could be of some help. Don't hesitate to ask.
Yours lightfully,
Benedikt