Here is a wonderful video by Sebastian Arce and Mariana Montes on the tango embrace.
Wonderful explanation of the tango embrace. Students of ours will recognize almost all of these explanations.. such as the idea that you don't take the embrace and then begin dancing, taking the embrace is part of the dance.
I just had someone ask me yesterday about when you take the embrace do you start with the open side or the close(d) side. First I respond to the woman. If she lifts her left arm and not her right, then I start with the close side (and vice versa). If she waits for me to initiate the embrace, then I will usually lift my left arm, so starting with the close side. Then, of course, I would expect her to lift her left arm so that we can take the embrace on the close side. Notice Sebastian do this at 6.33 of the video. BUT there are many nice ways to take the embrace at 6.22 he takes both sides of the embrace at the same time.
After a class with them in Baltimore a few years ago, I made significant changes to my embrace which have worked very well for me. The main one being not bringing my right shoulder forward in the embrace. I attempt to keep my chest very flat. Many leaders reach way around the follower with their right arm, bringing their right shoulder forward, and thus they end up leading with their right shoulder rather than with their center. As he says in the video, I bring my right hand around her and try to position my right hand in front of my spine. If we are leading from the center instead of from one side or the other then the lead will be very clear.