Judges are not keeping judging criteria a secret. All the things you work on in lessons? That's what you're being judged on.
Many officials hesitate to answer the "how do you judge ballroom dancing?" because there's no short answer. Even asking a judge why they marked you the way they did may not be an easy answer.
If you want to know what a judge thinks of your dancing, you may ask politely. If they can summarize their impressions into a short sentence, they will probably tell you. You should, however, be prepared to schedule a lesson with them, and listen (since you were asking in the first place).
The asking route is a much better and more educational and less annoying route than complaining about your scores and how certain judges "hate" you. Most judges don't know you, and if they happen to not like you personally, they don't hold it against you on the dance floor.
I am not qualified to judge ballroom dancing. I have no certifications or accreditations*. I only have 15 years of dance experience, about 11,000 hours of practice, 100+ competitions (some as a pro-am student or amateur, many as a pro-am teacher and professional), weeks' worth of coaching, and thousands of hours helping students improve their dancing.
This is how I prioritize my marks when judging [non-NDCA sanctioned] ballroom dance competitions:
This isn't a simple checklist, but a list of continuums that I find important. For example:
Waltz should look like Waltz, Rumba like Rumba, etc. A dance looks like a particular dance largely because of how it's timed to music. Timing seems like a forgettable criteria because it's so obvious. Ballroom dancing IS two people moving rhythmically to music.
If you are dancing off-time (or with no timing at all, on the left end of the spectrum), you will not get marked. I have seen several couples, uncontested, get 2nd place because they were dancing off-time. Yes. A second. To themselves. [Some of the new scrutineering software doesn't allow for uncontested seconds and that's makes me sad.]
I assume (with all the connotations) that if you're competing, you know how to dance the basic timing on the beat. If you cannot dance on the beat, you need to examine why you cannot:
- are your current steps (choreography) too difficult to perform at the correct tempo?
This is the most common problem and the easiest one to fix when it comes to musicality. It's also the problem couples are least likely to want to fix.
DO SIMPLER STEPS.
Doing "easier" steps might seem like a cop-out, a humbling experience, or a waste of time and money. But what's more humbling? Doing simpler steps, with ease, in time with the music, and showing the characteristic timing of a dance while continuing to work on your challenging routine off the competitive floor OR competing with your challenging routine and losing to someone who is choosing the first option?
The classic challenge: ask someone to watch your routines who hasn't seen them. Don't turn on music. Dance your routines. Ask them what it is when you are done. If they don't know, fix it.
- are you unable to hear the beats in the music?
First of all, are you listening to the music? Often, in competition settings, I believe couples often know how to, but they are caught up in THE DANCING or THE NERVES and have just stopped listening to what's coming in their ears.
So, you know... Listen to it.
Secondly, if you really have a problem with beat identification, the easy answer is to listen to a ton of music, clap your hands/stomp your feet, and count. Count all dances while you're on lessons, in group classes, and social dancing. Have your instructor count as often as possible. After a few weeks, this usually does the trick.
- are there certain songs or dances in which you cannot hear the music?
Dancers often have trouble defining the "2" in Mambo or a good Slow in Foxtrot. Seek someone to give you guidance in different ways to count (anyone know the Cha Cha trick for Mambo?). Find some obvious songs (heavy downbeats, lots of bass) from a music guru. Often, it's just listening to lots of music and counting counting counting like mentioned above.
- do you know if you are dancing on the beat...or before it?
I have seen many people dancing very confidently, off the beat. The confidence is admirable, but I'm often holding my breath and leaning back while watching them, trying to help them slow down.While it's never quite off-time, each step is jumping the gun and the momentum of each subsequent step seems to bring them closer to not-on-time. This is probably a problem in posture and consequent leg swing, but CHICKEN OR THE EGG.
- are you unable to control your timing with the music no matter what the situation?
Excitement, bad posture, poor muscle control - lots of things could be contributing to your lack of timing. Get thee to a professional.
On the plus side, if you know the accent beats of a particular dance and can perform your steps while accenting the correct ones with the music, that is nice. If you can make me think you have magically choreographed your routine to the song that happens to be playing, that is beautiful. (Note: those moments are a most likely a combination of luck, dancing to a particular song often enough to recognize it in a pressure situation, actually listening to the music, and good choreography... all which add up to... musicality.)
Next up: posture.
*Despite having taken many professional exams at two different studios and having the paperwork never sent in to actually get certified. Cursed. Neat.