There are so many things to focus on, it's not just one - learning, discipline, emotional fortitude, being organized, and so on, and so forth.
Here's a painful journal of what NOT to do. Again and again this fellow shorts the market, and is rejected time after time. He then adds size and shorts again, and again, and again... It's a good thing his wife has an actual job! There are definitely lessons here for new traders: https://www.elitetrader.com/et/threads/surf-report.306890/