I do things very strangely, and my way is not the best for everyone.
For me, over three years I studied the RWS, the THoth and the Marseilles separately. One card every day or so. I used a bunch of different books as references, tarot books, symbolism books, etc. There was a notebook for each deck, and I wrote down the various meanings from each book, and my own interpretations. This is not necessarily the best way for everyone (the Marseilles deck almost burned me out) but it helped me a lot, and deepened my understanding. I don't know about ever doing notebooks for any other decks even though it was a good exercise for me.
Now I am using one 78 card deck per week (two decks if an oracle or 22 card deck is on the list as well) and doing daily 3-card readings for myself. Writing them in a notebook. If deck buying stays steady at the current rate, and I keep up with it, I should FINALLY finish next year. (This started in, ulp, 2004). I wanted to use ALL my decks, yes, even the collectors decks.
I don't re-read with different editions of the same deck (regular vs LE deck, or a small vs. giant) but will with varital decks (Universal, Illuminated, standard RWS, Diamond, etc.). If I get a 78 card version of a majors-only deck I already own I use it separately.
After I finish this exercise, I still plan on using each new deck I get for a week, but I want to go back and re-visit some of the decks, maybe spend a month with each of the favorites.
The best thing to do is read. "Do three card readings. Do a lot of them." I am quoting Umbrae.
Practice, practice, practice. That seems to be the best way.
Most of all, make it fun for yourself.