My most successful (i.e., actually profitable) business model has been a low-cost carrier. I've adopted a number of practices from various real low-cost carriers, such as Southwest, Allegiant, and WestJet. Among them:

--Point to point, no hub and spoke
--Secondary airports
--Flights to airports which have limited or no service from mainline carriers
--Regional aiports with lower landing and handling charges than larger established airports
--Limiting IFS--if any--to inexpensive snacks
--No IFE
--Using one type of aircraft
--Maintaining low operational costs
--High employee/aircraft productivity

(Much of the above has been touched upon by various other, more experience AE members.)

Out of a desperation of sorts, due to the fact that I was having a difficult time being profitable, I simply went to Wikipedia and studied up on various low-cost carriers and noted what they do. I was pleasantly surprised to see how well it worked to copy their practices. I don't currently have any mega-airlines with twenty hubs but I enjoy myself and feel like I'm operating relatively realistically.

Also, somewhere in one of these forums I found this suggested formula for acquiring aircraft; it works fairly well for me, although I sometimes stray away from it:

After cash reaches $5 million,
1. Lease used aircraft until $15-20 million
2. Lease new aircraft until $25-30 million
3. Buy used aircraft until $150-200 million
4. Buy new aircraft

Or you can just IndiGO it and not operate more than two types of aircraft even though you have 40% market share. Worked in my first airline, but that accidentally got deleted

Hi, it would be really nice if we could start a group airline with more than 2 people controlling it.