My observations, YMMV... The single most important technique which the vast majority of partner dancers don't know or are inconsistent about doing is alluded to in these videos. at 4:18 at 3:20 The ability to maintain a taut/flat lower ab and a butt that's tucked under the torso is essential for good upper and lower body coordination. This straightens the body line, making the body like a pair of chopsticks with flex, directing energy and force with maximal effect (and hence minimizes the work). This is the "primary effort" a dancer should make. Although most (serious) Ballroom dancers have probably heard of the idea of axes of rotation, many/most don't manage to attain it (consistently) because of lack of understanding of the above. An uncontrolled ab or protruding butt breaks the axes lines, making it hard/harder to rotate or lean/sway. Unfortunately, because many dancers are more into the "look" and pizzazz, they often miss this most fundamental of techniques, either because they were never taught or exposed to it, or because they never figured it out for themselves. How do I know this? I am a prolific social dancer and I observe a lot of dancers in action. At this point, I can tell from the movements of my social partners of the moment how well they coordinate upper and lower body actions and can "superimpose" myself onto the dancers I observe to figure out the force vectors they employ, and consequently how much excess work they do. Because the connection between partners is pretty much always above the waist, and typically at the hands/arms, the ability of each partner to extend that connection across his/her own body so that the legs+feet which provide the weight-support are integral and consistent with the inter-partner connection, both in position and timing, is key to how pleasant and easy the dance goes. IOW, when a partner shifts the connecting point one inch, what he/she desires is to have the other partner shift his/her foot/feet a proportional distance/direction, with appropriate time skew. I consider Ballroom Samba to be the most difficult dance to do with real lead+follow and connection. Few Samba dancers can do this, and the primary reason is because most others have poor grasp of abs/butt control. When a partner executes a body gyration, the idea is to carry it throughout the body, but most dancers end up flailing the upper body separate from the lower (especially with disproportionate butt shaking), making it "impossible" to do good/true lead+follow (no connection from one partner's feet to the other's). Consider the following figure, the Closed Rocks... Although doing an acceptable demontration (I will be critical here to press my point), the dancers are not using enough abs/butt control so their upper and lower bodies are disjoint (bellies are flopping). There is no energy flow from the feet of one dancer to the other, and the dancers are in each-other's way (because their dance axes are not "straight enough"). The leader can't convey to the follower to "get out of the way" (at the hip), so there's in-fighting. Unfortunately, most dancers dance Samba (and lots of other dances) using patterns/amalgamations rather than individual movement/weight-change, which means a lot of mediocre/bad technique is covered up. A Standard-only dancer who understand/uses abs/butt control technique should be able to do Samba basics ad-lib. It turns out that for a lot of activities, such as skiing, skating, scuba diving, and gymnastics, being able to straighten the body, so upper and lower parts are integral, is key to basic competence. Because these activities are primarily characterized by performance/balance/control rather than appearance, participants tend to gain awareness of the need for abs/butt technique as a natural outgrowth of doing. In the 20+ years I've been taking private/group classes in all sorts of partner dance, I have never heard of any instructor mentioning the abs/butt technique. Instructors talk about "posture" but don't mention the important details of how to achieve it. In the 3 or so years of classical dance lessons I attended, I learned implictly to use this technique at all times, as the 45 minutes out of every 1 hour lesson doing bar and floor exercises demanded the ability to keep the body straight. Every competent Ballet/Jazz/Tap/Modern/etc. (solo) dancer knows this (as shown in videos above). Although I had become keenly aware of the need for partner dancers to do this fairly early, particularly in Samba, it's only in recent years that I would categorically state that in _every_ partner dance across the board (of the 35+ dances I do), this is a core/foundation technique (now that I understand even better "why"). To be clear, the abs and butt techniques shown in the solo spin videos are only part of the story. For partner dancing, the technique has to be refined with such things as body rotation, how much strength verses habit, how much play there is between upper and lower body, etc.. While this is necessary for the partner dances and classical solo dances, it is optional for other solo dances such as line dancing, since the body dynamics are different and these other solo dances have so much more random freedom. The abs/butt technique gives rise to so many other good/great techniques; trying to do these other techniques without this core capability would be a futile proposition.