What did you do the times you bankrupted? Where did you hub, which aircraft, which routes, how much advertising?
What I have done in both NAC and ATB2 is hub at a relatively large airport, start a general worldwide marketing campaign in all media, and decide on an aircraft type. In NAC I decided on a short/medium haul type and started routes <1000NM from my hub, no second-leg routes. In ATB2 I decided on a long-range aircraft and started longer routes with short routes in between to maximize aircraft utilization, no second-leg routes. Then I accidentally acquired a second fleet type for short-range operations, which has been surprisingly successful so far.
Generally I am trying to look for routes that are not already served over capacity, ideally I would be the only airline on the route but usually that situation will not last for long. I have not changed my ticket prices at all from the default pricing and otherwise I am also pretty much running on automatic/default settings. It takes some effort to acquire new aircraft, I have not figured out if there is a pattern when the used aircraft market is replenished so I check the market regularly while doing other things on the computer or even doing something else at home.
I have taken out several loans as needed in order to be able to expand fairly aggressively, as I think it is important to gain new routes, reserve slots, and generally be bigger than your competition early. Patience has been mentioned as a key factor in succeeding in this game. To me it means sticking to your initial plans, as in waiting patiently for the right aircraft to come along instead of just leasing anything in a panic. It also means that sometimes, when you are reasonably sure you are making money, it is best to just log out and let the cash accumulate.