There's a lot to learn about managing your money in your 20s.
But if you have to focus on one habit to master first, the choice is simple. The most important thing to learn is to live within your means, says certified financial planner Carolyn McClanahan.
"As soon as young people start making money, they tend to start spending it all," McClanahan, the founder of Life Planning Partners, tells CNBC.
"You have to establish the habit of spending less than you earn. Once you create the habit of saving, it stays with you for your entire life."