I have only been playing for about a week, so I'm not totally sure about game settings, how ever I have figured out this.
I started a route where 2 airline's were in competition already. On the route planning, thumbing through route options etc, I somewhere found an "average" price for the route (considering the competitors). I have not been able to find the average price since.. how ever it helped me then.
To enter the market, I put myself 20% below the average, but only 1 flight where I could have capacity of two according to demand. I also started Route Spesific Markting on all channels but only for 1 month (so it doesnt cost too much).
Once my seat factor started getting more then 50, I started raising prices 5$ a week until seat factor increase almost stopped. Then I put it down 5$ again. So far my SF has been stable around 80-85% even after starting two flights. Route image is still at 75 and I am still marketing the route.