One of the keys to a successful and enjoyable class for everyone involved is that one should avoid giving feedback to their partner unless the teacher specifically says to do so. Even if you think you know what could 'fix' the person you're dancing with, it's best to avoid the situation. Often times, the person giving feedback ends up interrupting the teacher addressing the point that you're trying to address. A good teacher sees the problems that are happening in class and addresses them for the benefit of the entire class. Teachers are keen at seeing issues and finding ways to fix them; it's our job. Also, consider that the teacher is perhaps choosing to leave something unanswered on purpose. It could be off-topic or if the target student(s) seem at a limit of learning, it could be best left alone.
Look at it this way, if you're talking to your partner (about anything) you're not only disrupting yourself, but you're also disrupting your partner. Not to mention, the couples to the right and left of you who can't fully hear what the instructors are talking about because you're talking (yes, whispers too are disruptive). By this time, the teachers most certainly noticed that there's talking and general distraction is going on in the class and they too are distracted. So by trying to be helpful to your partner you're actually being quite counterproductive as you've distracted somewhere in the neighborhood of 8 people.
If you're the target of this unfortunate occurrence, your best weapon is "Thanks, but I really want to hear what they [the teachers] are saying right now." or Perhaps, "Actually, I'm working on X right now but I'll keep your suggestion in mind." Or "that's interesting, Let's see what the teacher has to say."
If you [the feedback giver] still think that the teacher has missed something important and something needs fixing. Let the teachers handle it. It's their job. In most classes ample opportunity is given for question asking. Ask the question. You could prompt an interesting discussion or better yet, entice the class to ask more questions.
In one simple sentence: Don't do it. It's rude. More often than not, people go to a dance to... well, dance. They aren't in class. They aren't in practice. They aren't taking a private lesson from you. They're at a dance. They want to dance and have a good time and just happened to ask you (or be asked by you) to dance. Don't be the kill joy that traps some poor, confused beginner and tries to 'teach' them something. Also, unless you're a teacher and know what you're talking about, you are just calibrating that person to dance with YOU better. Instead of blaming them on all of the short-comings of the dance, think to yourself how can I make this dance better? What can I do to accomplish what I'm trying to do. Don't always assume it's your partner that's the problem. Look inward first. If you're still bent or they're doing something that's physically painful to you voice your concern toward yourself EXAMPLE "I'm feeling my arm being twisted uncomfortably."
If you're working on material from a recent class and the teachers are present, grab them and ask them for a diagnosis. Most teachers would especially like to clarify what they meant if you're confused about a recent class that they taught.
Not everyone has your same taste in cologne, perfume, or body spray. Some people have sensitive allergies that could prevent him/her from dancing with you and that would be TRAGIC! DO use deodorant, but DO avoid cologne, perfume, or body sprays before dancing.
Also, along these same lines, DO shower and use deodorant. This goes for everyone, but even more so for the taller guys. Girls that are shorter (imagine - nose at armpit level) might be sad if you bring her into closed position and you're not fresh.
Mints - they're generally available at dance venues. Use them. Not everyone wants to know the details of what you had for dinner.
Smoking - If you smoke, please allow sufficient time after you indulge to air your clothes out and grab a mint on your way back to the dance floor. This too can trigger unpleasant allergies in people.
Bottom Line: Don't let personal body odors (choice or circumstance) be the reason that people don't want to dance with you. Most often, we're not aware of our own body odors, unless they come in a bottle that we spray on. Play things safe and follow the above guidelines for maximum dance enjoyment!
Although dancing is athletic and sweating is expected there are a few things to keep in mind. If you sweat a lot, bring extra shirts. [Yes, I meant that to be plural] Depending on how much you sweat, plan on bringing a sufficient number of shirts so you can remain dry. It is also nice to have a small towel to occasionally dry off. Remember to dry your arms off when you change shirts so your partner doesn't just slide away from you. This goes for ladies and gentlemen. GASP! Girls sweat too?!
Girls, I have to bring up open backed shirts. We sweat everywhere, not just in places where we wear clothes. Try to avoid open-backed shirts so that you don't slip out of your leader's hand due to a sweaty back. And would you want to grab a sweaty back with every swing out? I don't think leaders are overly fond of it either.