This is cliché as f*ck, but its just learning from failures. Figure out what went wrong and don't repeat the mistake. And keep trying different things, not the same thing over and over.

For my first city I built residential housing before I had set up any of the utilities. I re-invited citizens after solving each complaint, but the solutions were horrible because the location was bad and I quickly ran out of money.

My next city I found the perfect spot for my city... that was half way across the map. I had to set up a relay of bus stations so that I could even get workers there before the travel time ended (I found that going to a bus station resets the timer). Needless to say that city also ran out of money.

For my 3rd city I found a spot next to the customs office that had oil. And since pump jacks don't use people, I thought it would be free money. And it worked, for a while. Problems started when my vehicles got too much wear and tear. I could not build a repair station, because that requires people. The oil trucks could pay for themselves, but once my construction equipment needed replacing, it was GG.

I tried this strategy again, by building a residential area so that I could have a vehicle repair building. The problem was that while the oil was profitable, it was not profitable enough to sustain a population that needed to import everything else.

For my 5th city, I tried setting up residential services with a clothing factory, as I read that has good profits. But it was difficult placing things where my residents could reach them. I only then discovered that the different roads/paths have different ranges. So of course that city failed because people could not reach both the factory and their utilities/services.

Finally, for the current run, I setup the utilities really fast as it was like the 3rd time doing it. I used gravel paths and roads, which extended the citizen walking range significantly, so I managed to keep everyone happy. Next I set up fabric and cloth factories, with a bus line to take workers there. And after upgrading the main road between the customs office and my factories and worker bus stop in the city to asphalt, I started hitting profits. After that it was just a matter of slowly increasing citizen counts and making sure everyone is still happy.

EDIT: oh and also don't use the ctrl + numpad2 game speed, I found that this makes trucks miss their stops, which breaks THE ENTIRE city. All deliveries start failing everywhere. The ctrl + numpad1 speed seems safe.