Looking back, here's what would have saved me the most time:
Your sphere is your business. Not Zillow leads, not door knocking strangers — the people who already know and like you. Start there and stay there.
Learn to be comfortable with silence. Most new agents talk too much. The best thing you can do in a buyer consultation or listing appointment is shut up and listen.
Track everything from day one. Calls made. Appointments set. Contracts signed. If you don't know your numbers, you can't improve them.
None of this is complicated. Most people just don't do it consistently.
What's one thing you wish someone had told you when you started?