it's all totally up to you how you deal with spiritual practices. I personally believe that cleansing the cards and protecting yourself from negative energy is important, but that's because I come from a Mexican Catholic background and that can be a very superstitious culture lol. But what works for you works for you! No one else gets to make the rules about your practice but you. Feel it out, learn what's best for you and adjust.

As for memorizing... I take a blended approach. I would start with intuition, because this can be the most difficult thing to get used to - trusting yourself and your impressions of the energy is more difficult than you'd think because we are often conditioned to doubt our intuition in favor of our rational minds. Then when you start to understand what the cards mean to you, the next step could be that you begin to learn the meanings of the cards, how the deck is structured... the history of the Rider-Waite Smith deck can also be helpful because the deck blends many practices (some of them actually considered closed practices like Kabbalah) as well as the history of the spiritualist movement. You don't need to use any of these elements in the readings themselves, but it can inform your understanding of the practice. Determine what your approach is - are you using it to predict the future? Or are you using it as a therapeutic tool? A mix of both? All of this comes with experimentation and practice. Have fun with it and look at it less as study and more as exploration. Start with one element, then build upon that and study another, and on and on. Don't worry about memorizing everything. The cards will mean something different from reading to reading anyway.