The best way to communicate with domestic cats is through your entire body language coupled with touch. Body language and gentle petting (stroking normally) is a language which domestic cats understand very well. Speaking to cats can also help but the sounds we make are only an adjunct to the more important body language and petting. Cats will respond to warm friendly sounds. They don’t respond any better to sounds intended to mimic the domestic cat’s meow. Don’t think that cats understand humans when they meow at them. They don’t. Cats will understand the sound of their name when you call them. But it is a recognition of the sound not of the name itself.

Dogs communicate with people very effectively by using their whole body language. They are constantly signalling with body language from the tip of the nose to the end of their tail. And people can read dogs very well but the same applies to cats reading humans in my opinion. Perhaps, sometimes people forget this.
If we are anxious, and a lot of people are anxious nowadays, our behaviour and body language changes. We might become slightly short tempered. Domestic cats recognise this and it does affect their behaviour and the relationship.
Conversely, a confident, relaxed and calm human who creates, through their body language and demeanour, reassuring signals to their cat that all is well fosters contentment both in cat and person.
It’s about whole body language an even wider, the general ambience of a place, all of which are generated by the occupant of a home and the caretaker of their cat. Of all the methods of communication, the most effective is petting your cat. This mimics one cat grooming another and a mother grooming their kitten. It is called allogrooming. So cats do it to each other and therefore if we do it to them they fully understand it. It is an act of friendship and a behaviour which cements the bond. It should be done gently with loving sounds within a warm ambient environment. And cat guardians should discover through trial and error what their cats likes the best. That’s quite important.
A lot of what we can do in communicating with our cat is to lower anxiety levels. I have this concern that domestic cats may tend to be more anxious than we care to imagine, unless we do our bit to reassure them. From my perspective, therefore, a lot of communication between me and my cat has the purpose of reassuring him, to make him feel confident and relaxed. Human-to-cat allogrooming gets the job done. But it must be done within the context of handling domestic cats properly at all times and generating routines in the home which domestic cats like.
Rhythms and routines are also forms of communication from human to cat. And it applies in the opposite direction. Cats have a different biological clock to ours. They can be more active at dawn and dusk and perhaps during the night as well. They are less active during the day time, although these boundaries are blurred because they are very adaptable. But their rhythms are slightly displaced from ours and therefore humans should try and fit in to their domestic cat companion’s rhythms as well as cats adapting to ours.
P.S. These are my personal thoughts. I have not referred to textbooks on the subject to write this article. It has come straight out of my head and it is largely commonsense based on years of living with domestic cats.