I’m a little surprised by how many people chose #1. I vote for #2. I play tons of different kinds of decks, really getting a feel for the entire card-set, which is no small task at this point in the game’s development.
More generally speaking, research show that it takes lots of practice to get good at anything, so repetition will aid growth in any subject. Natural talent/skill can reduce the total amount of time it takes, but you still just have to play a lot. Some of the best players in my local area have been playing card games for years, and all of that practice promotes better play regardless of the game.
Other things that have helped: playing against people who are better than me, and picking up on the tricks that they use or moves that they make, watching videos on youtube of people playing, and to a lesser extent reading about it on forums such as stimhack.
Edit: I would also suggest skipping deck building to start with. Deck building is, imho, the hardest part of the game, and it’s easier to start with a deck that someone else has shown works well and simply practicing with that first, learning why it works, before then applying those principles yourself. In a similar fashion, deck-building is like learning to cook. Nobody starts off cooking like Gordon Ramsey. You start by following a recipe in a book, step-by-step. Once you get the basics down, you move on to step two by following a recipe but adding in your own spices/ingredients to make the dish suit your personal tastes. Once you mastered that you move to step three, which is creating a recipe yourself from your accumulated knowledge/experience. There aren’t hard lines between the steps, you just gradually get better until one day you find yourself saying “Honey, how about duck tonight with plum sauce and some nice spring vegetables?”