Before launching into the full details of the Cardăsda language, it's wise to go over some of the basic etiquette rules in Cardassian society that will go a long way towards conveying your earnestness and respect for those whose language and culture you're studying.
Here is a small sampling of the indicators you should take care with:
Physical contact and proxemics
As with many cultures, Cardassians value their personal space, and to intrude upon this territory may provoke discomfort or even hostility. This space, however, is considered to extend further than some students may expect, and to violate that boundary could unwittingly convey an impression of anything from boorishness to threatening intent.
It is generally advised to allow at least 1.5 m [appx. 5 ft.] between you and a person you are meeting for the first time; more is not inappropriate as long as both parties can comfortably hear each other (more on this topic later). Conversely, do keep in mind that a Cardassian's decision not to approach you closely should not be interpreted in isolation as a sign of standoffishness--rather, the respect of your personal space often signals willingness to reserve judgment and come to know you better. This is a common mistake that has often led to people from cultures that accept smaller amounts of personal space to get off on the wrong foot with Cardassians in spite of what the Cardassian regarded as a respectful approach.
Most importantly, though--unless the other party initiates the gesture, do not ever introduce oneself with any greeting ritual that requires physical contact, especially between opposite sexes. Cardassian propriety forbids physical contact between man and woman outside of the context of engagement or marriage, and especially when initiated by a foreigner, any violations are likely to be taken as insults.
Ritual embraces, kisses, handshakes, and any similar greetings are strictly off-limits unless invited by the person you're speaking with.
You may find that some Cardssians will disregard these rules for varying reasons; it is very important to read the context of the situation before letting instinct take over.
Do accept if a Cardassian greets you with the ritual of your culture: this is a sign of respect that should never be snubbed, and should be repaid at the soonest appropriate moment by demonstrating your own respect for their customs.
However, as a foreigner, you may encounter individuals who intentionally violate your personal space as a means of intimidiation. Where the situation does not appear volatile, it is best in such cases to calmly assert for yourself the amount of space this person would be expected to provide for another Cardassian: maintain your posture and level of eye contact, but without comment, simply take a step to the side as necessary.
While not as elaborate or nuanced as in many cultures, the bow has a prominent place in Cardassian etiquette. Varying from a slight incline of the head to an actual bend of the waist, the bow is used to greet, signify thanks, and obedience--in that order from shallow to deep. This position is generally held for anywhere from less than a second to up to three--the longer the bow, generally, the more distance in rank or age between speakers.
Unlike some Earth cultures, once is enough under almost all circumstances. Furthermore, in informal circumstances, it is perfectly acceptable to maintain eye contact with the other person--and preferable once a favorable relationship has been established.
[NB: Watch Garak and you'll get an idea of the mannerisms I'm talking about--it's definitely far subtler than, say, in Japanese culture, but it's there.]
Age and youth
Cardassians confer great respect on the aged. They do not typically hide signs of aging--in fact, they are seen as marks of dignity. Seniors and the elderly should be afforded the utmost respect at all times, and students should always use the most respectful forms of address possible unless absolutely instructed otherwise by the other party.
Part of that respect is to avoid circumlocutions when referring to the other party's age. Adjectives such as "older," "senior," "mature," and even "ancient" when speaking of the very elderly are appropriate and respectful. In fact, after a relationship is established on pleasant terms, you may even ask a Cardassian his or her age--if you believe they are older than you. And yes--that goes for women too.
Similarly, make an effort not to show embarrassment at any features you have that may indicate age. The fact that a Cardassian seems to visibly note your wrinkles or grey hair is not an insult (and may even be a sign that your words will be treated with the respect due towards age). Don't refer to any such embarrassment. Nobody wants to hear you agonize over your first grey hair or wrinkle, or your dread of your 70th birthday. (Especially note that on post-Dominion War Cardassia, your perceived inability to be grateful for a long life may come off as particularly insulting given the extreme number of those within the Cardassian Union who will never reach what are referred to as one's "summit years.")
Finally, don't refer to a Cardassian's youth unless you are very clearly speaking of a young child. What may seem like a compliment to other cultures--praising a person's "youthful" looks, energy, and so on--instead conveys the idea that you don't take the other person seriously. Especially when dealing with Cardassians in positions of responsibility, you do not want to mistakenly convey any impression that you feel he or she is not yet mature enough for his or her position. Speaking of youth should be treated with the same caution as speaking of age in many Terran societies.
Cardassian hearing: do's and don'ts
It is acknowledged fact, by both humans and Cardassians, that Cardassian hearing is the slightly weaker of the two (the contrast with Vulcans, of course, will be even greater). It's for this reason, many linguists believe, that certain "redundancies" exist in the Cardăsda language, to provide more opportunities for grammatical cues to be heard over background noise.
Humans and other species with greater frequency and decibel ranges should be aware, though, that there are proper and improper ways to address this disparity.
Do, if carrying on an untranslated conversation in your native language, make an effort to eliminate regional accents that may make you unclear to someone speaking Federation Standard as a second language. Enunciate clearly, taking care to avoid things like dropping consonants or making your vowels indistinguishable from each other, but do not exaggerate your speech.
Do not speak any louder than you might with anyone else with the same ambient noise level, unless you are specifically asked to do so--raising your voice unnecessarily is quite rude. Similarly, only move closer if invited. It is, however, a wise idea to make sure that if you're in a fairly noisy environment, that you are facing the person you're speaking to--especially with untranslated conversation in either language (where the other speaker's comprehension or your accent may interfere, respectively)
Respect individual experience
Finally--and this applies to all cultures--respect the fact that no non-hiveculture is monolithic, even where governments have made active attempts to bring that about. While these guidelines will generally work, remember that the upbringing, personal experiences, and even some of the customs and opinions may differ. The experience of a Nevotda vintner certainly will not be the same as that of a career military officer from Upper Rivçal, or the resident of a recently-settled rasgălor (outworld).
And though it's hard to conclude a list of do's and don'ts this way...do look at most interactions as an opportunity to establish amiable relations--and if you're fortunate, sound working relationships or even a friendship.