Years ago, I spent a lot of time giving free readings online, which was very interesting and required a kind of apprehension of my intuition that couldn't be faked with visual/aural impressions about the querent or casual prompts for more info. I had to look within to get the reading right. And being online, anonymous and free, it was a fairly no stress environment. I could make mistakes and so what. I had to suck it up and have enough courage to try. I found a voice inside that did the reading for me, and I learned, at least at a rudimentary level, to trust that voice.
These days, I find very helpful posing rather specific questions regarding my own life/development, and carefully documenting in my diary the spread and my interpretation of it. This is particularly illuminating as I look back at the readings weeks or months later. It seems the cards are always more spot on than my interpretation was at the time, and, with the benefit of hindsight, I can apprehend where my readings went askew.
I have long used the Celtic Cross, but am committed to also deploying the spread outlined in Liber Theta, which Temple of Thelema has made available for free. You can get it here: www.thelema.org/publications/. It is a wonderful and authoritative little guide.
And I'll second the suggestion that meditating on the cards without a lot of study or wordy interpretation is invaluable. These are archetypical images, after all. Something about just sitting with the image is both powerful and informative. Another slant on this is, particularly with the major arcana, to put yourself IN the image. Be the Fool, experience his naive vertigo and heady optimism. Be the Magician with the swirling, scintillating implements all about. Be the Chariot, with its whirling grail and forward thrust. Be the Tower, feel its concrete integration crumbling and wrecked. You get the picture (so to speak). Let the imagination of all your senses run with these meditations. Feel the weight of the Emperor's armor, the warmth radiating from above to your left as you sit cross-legged on the throne, smell the musky scent of his rams at your side, let your gaze look right to your beloved Empress. Set the timer, and build up the image as much as you can in that time. Then write down your impressions in your diary, and, over time, you will build up your own lexicon of the cards.
I have bought and read a lot of books on the Thoth deck. They are useful, at some level, but after I started meditating directly on and "in" the cards, all the excess verbiage in these texts became something more of a diversion.
Also, consider this an adventure that will last the rest of your life. Baby steps count. Just be steady. Be diligent. Keep at it regularly. You have to build a pyramid one brick at a time. Be patient and persevere. And have fun!
Happy journeying.