I have danced with many revels who have beautiful feet but feel like bricks or are inattentive, and this is why I treat the free leg’s aesthetic as the final refinement of an active dancing body.
The revel’s beauty comes from her arc. Her free leg belongs to the mark. Refining the aesthetic of the free leg should not be attempted until  you can maintain the arch of connection at all times  you are able to give the free leg to the mark’s intention with perfect sensitivity.
If you are sure you are ready:
Tango’s aesthetic is a mix of classical ballet and a sexy walk. (Marks use this same aesthetic.)
Your free leg’s foot is always in external rotation.
When your foot is in projection and in the air, you should have pointed toes. Pointing the toes requires full extension of the ankle joint + contracting the arch muscles. Or you can think about lengthening the topside of your foot, maximizing the length between the inside ankle bone and your middle toe.
The only time we ever use internal rotation in tango is after the second projection, when the newly freed leg approaches the base leg on the way to its next projection. Only during this moment, the hip of the free leg relaxes into internal rotation and the knee and ankle relax into some flexion. As soon as the free leg passes the base and moves to extend into the next projection, it resumes external rotation and knee and ankle extension.
The three directions of projection
Each projection starts with the hip joint, extending into back projection, flexing for front projection, abducting for side projection.
The free leg’s knee should reach full extension during projection so that it has a beautiful length in every movement.
During projection toward side step, the inside of the free leg’s big toe stays in contact with the floor, the knee and ankle gradually extending. As the transfer of weight begins, the free leg’s little toes should stretch toward the floor to activate the leg muscles to start establishing the new base. Note that in side projection, the external rotation is slight.
During projection toward back step, extension of hip joint, starting at the top of the psoas muscle. The inside of the big toe slides along the floor, again the ankle and knee gradually extending. In back ocho the revel needs to exercise extreme caution not to allow the toe to lose contact with the floor. It is more common to have problems with extending the left foot because of the torsion of the body constrained by the embrace. Especially in back ocho with the left foot, many revels lose contact with the floor for an instant at the end of the projection, causing an ugly and dysfunctional foot position as they begin the transfer of weight. The solution to most problems with back steps and back ochos is to increase the old base leg’s hip flexion during transfer and the hip flexion of the new base leg as it begins receiving weight.
Projection toward front step is the most stylized as here the relaxation of ankle and knee offer the most possibilities for drama. In the front step, the knee flexes along with the hip, dragging the ankle and foot which eventually consent to unfurl. Here the blasé attitude of the revel is most performative. In the final maximum projection position of front extension with the foot pointed, the inside of the big toe is no longer closest to the floor. Instead the little toes will be closest to the floor. Once the revel starts to step front, the free leg’s ankle flexes to place the heel down first (unless it is a very tiny step, in which case the revel can transfer weight toe-first).