What should one concentrate on if they strive to get better at social Argentine tango?

Well, I will start with the least important thing. Figures. Steps. Patterns. People go to classes and collect them. But executing figures while music is playing doesn’t necessarily constitute dancing tango. 

For it to be dancing tango, there are certain other elements that are required.

* there should be a relation between the music and movement, and I don’t mean just the (main) beat, I mean the mood, the power, and the dynamic of the music should be reflected in the dance.
* there should be communication between the man and the woman. The man doesn’t “make” the woman step or stop, he leads her to step or stop on her own.
* there should be communication between the couples on the dance floor. Dancing like you are the only couple on the dance floor is disrespectful of the others and possibly dangerous (unless you are the only couple on the dance floor of course).

what about technique?

while certain elements are valid across all types of Argentine tango (milonguero, salon, stage, nuevo), some techniques are more important for certain types and some techniques are incompatible between types.  But regardless of this, technique is important to dancing, it will make you stronger and better able to handle the challenges that will come your way.