Just making more shots is going to help. Marcus Smart and Kyrie Irving are bound to regress up to the mean of their normal averages. That, right there, would add 3-4 points a game.
I think Terry Rozier has the potential to keep upping his percentages as well. I'm maybe one of the few left that thinks that Marcus has the potential to have a normal shooting average (40%, 33%, and 75%). The development of these two would add another 2-3 points a game.
Combine that with Brown and Tatum's continued development, and CBS finding rotations where the offense doesn't dip as much, and we'd look a lot better on offense.
I think internal development is the key right now. Finding an offensive player who can also play versatile defense is difficult. Getting an offense-only player (Lou Williams, for example) would throw our entire scheme out of whack.