Try to minimize costs for stuff such as transit, education, etc.
For example, instead of making a shit load of roads and bus stops try to make it more efficient. You don't need a fire station early on and a police kiosk will do. As for schools lower funding so it has enough spaces but you aren't paying as much. Also parks are really nice but don't overdo it as it has a monthly cost as well. When your city is small you will be loosing money unless you don't have stuff like schools, fire departments, police stations, etc.
Only when your city gets bigger do you start to make money. But remember the key thing is to make it efficient! Make sure if you build a school that it will work later on, and not so you need to build another one and pay more.
Also you can raise taxes slightly.
