1. What’s the biggest mistake beginners usually make?
In crypto trading, one of the biggest mistakes of most beginners is that, they thought that it's can make them rich very quick, and because of that, they wouldn't be patient to learn, and follow the due process of learning that a beginner requires.
Furthermore, the mistake of most beginners is that they don't trade with what they can afford to lose, instead they trade with what they can't afford to lose, that is why you will see a newbie trader jumping in and out of a trade in a losing position due to panic or fear.
2. Any habits I should build early on?
The only harbit I would advice that you should build on is to be taking less and more quality trades, than many random trades that will result in losing more than, in other words, go for more quality trading set up, even if it's only one trade in a day, it's a lot better than trading many of it that wouldn't end well for you.