Jaylen has looked really good.
It's a 3 game sample, though, so hard to draw conclusions about what it is that he's doing better and what is sustainable.
From what I've seen I think we can expect the following things:
1. Improved decision making on offense, less whiffs when there's an opening that he can pass to and less reckless offensive possessions to increase his ball security.
2. Crisper passing, higher "good" pass conversion rate and the occasional high leverage pass like the bounce pass to Hayward against the Raptors to, unlocking high value open looks near the basket for his teammates.
3. Sharper ballhandling, less fumbles when trying to create his own offense and the use of advanced moves to break defenders off the dribble for easy looks as well as fouls to spike his scoring efficiency.
4. More methodical approach on offense by going at different speeds instead of only one to confuse defenders and open better looks for him to pass/shoot/dribble.
I'm expecting a big season from Jaylen Brown with these improvements to his game, I think he has the foundation to churn out a solid All-Star season, or even a low level All-NBA season if he can continue to hone on his skills and approach to the game as the season progresses.