Also don't jump on already overcrowded routes thinking that by lowering prices and slapping on frequencies that you'll take business away from a legacy carrier with a high CI and young fleet.
Actually, all my routes (3) had plenty of room. I had to go bankrupt, but started again at the same base, but this time with a 737-300 and a 737-400. I think the -200's were killing me last time with fuel. I'm not one of those that would overcrowd a route unless I'm pretty sure it needs service (Or go in knock down another carrier a few pegs once in awhile, and that has worked more often than it hasn't. Again I don't do that as rule unless I know I can get away with it, LOL)!
Another thing I do is go into a market very stealth-like. No announcements or anything but a simple marketing campaign or two. So I go under the wire, so to speak, and it usually winds up too late for any other carrier to figure out I've started service. All of a sudden I'm just there with a 1/3 market share. ("Where did he come from??") But again, I'm careful about that one.