Nina Tatarowicz from Tango Elixir on tango alignment:

Letʼs look at our Tango Alignment from the ground up. So starting with the feet:
We always make sure that our weight is on one foot or the other.
But how can we be sure that weʼre stable?
Try to find the connection onto the floor from the big toe root, the little toe root (which is your metatarsal: this band, but on the other side of my shoe) and the center of the heel. So, for followers, itʼs a little more challenging because of the stilettos, but both followers and leaders need to find that triangle connection.
So we have:
We change weight, ground, and think about spreading: so itʼs like, going in opposite directions, itʼs spreading. Spreading your foot to create that sense of grounding.
Keeping the ankles together, and making sure that you release the other leg. The knee comes in. The knee comes in: we donʼt keep it out– boom– it relaxes in.
We need to make sure that the legs stay springy, so making sure that thereʼs always a sense of bend and compression. So that theyʼre never locked completely back, and theyʼre never completely bent down where thereʼs no life. Always a little bit of that resistance.
Depending on your style, it can be more lifted, or it can be a little bit more bent. Also depends on the size of the step we want to take.