The initial stance for the Tango uses a parallel Third Foot Position, with the left foot slightly in advance of the right. To properly achieve this stance, stand first with the feet together, knees flexed, and body carried squarely upright from the hips. Shift the weight toward the balls of the feet; rotate both feet about an eighth of a turn to the left, simultaneously sliding the right foot back until the toe is near the arch of the left.
The feeling this should create is that the body has achieved a leftward "torque," with the right side of the torso very slightly in advance of the left. A popular analogy is that of a dishrag being twisted dry, but obviously your body will require much less torque than that.
In order to maintain this torque as one moves, forward walks with the left foot will be taken in CBMP, while forward walks with the right will be taken with the right side leading; conversely, back walks on the left foot will be taken with the left side leading, and back steps on the right foot will be in CBMP.
As a consequence, the walks will curve to the left. More torque equals sharper turn.
In order to achieve these foot positions, the feet are lifted very slightly from the floor and then placed in position, unlike the skimming foot movement of the swing dances. Please don't overdo this part. Only lift the feet as much as you have to.
The transfer of weight from one foot to the other is staccato, with a feeling of getting completely off of one foot and on to the other; the weight is not divided between the feet at mid-stride as it is in the swing dances. The feeling should be crisp, light and decisive, without any rise and fall.
Proper execution of this technique will produce a dance that is strong in character from the very first step.