Astrology, alchemy, kabbalah, numerology, elemental dignities, the "theme" of each deck (paganism, Grail lore, gnosticism..) - there is no end to the material you can learn to find new depth in your readings. I tend to do these things in waltz steps - 1,2,3... and 1,2,3...
Step 1 is just enjoying the images and finding inspiration by them, by colors, shapes, obvious symbols, position of viewer. Each card tells a story.
Step 2 is remembering all the theoretical knowledge I know about the card. Esoteric symbols, astrological and elemental associations, position on the Tree of life, number symbolism, color symbolism - whatever is helpful and seems relevant. Especially important: the personal meanings cards have accumulated for me over the years.
Step 3 is putting everything together: spontaneous reaction, personal context and theoretical knowledge.
And then I forget everything again and start again with simply looking at the picture. And I'm with Step 1 again....
Everybody finds his own style. There is no pressure - it takes time to absorb the knowledge, and some of it escapes again and again, like water between the fingers. I have to conquer it again and again.
Other things come by sudden insight - all of a sudden I feel that I understand numbers now much better. How did that happen?
Don't feel you have to learn a system if you don't want to. You can be a perfectly good reader using your intuition and the messages from the images themselves. It's like learning a new language - some people enjoy knowing the grammar rules and applying them, others do it instinctively and find too much grammar confusing.
Find your style and enjoy the journey. It's wonderful to spend so many years with tarot cards and always feel a beginner! Like a marriage that's still exciting after decades together!