have to adjust them a little here and little there?
I re-set them to default every real life day, to get the inflational increase, and in later games when fuel is a b*tch to get the higher prices due to them being tied to fuel as well.
It is pointless to reduce the fares in the beginning, because LFs are always crap after starting up, or running on a new route, just keep the prices the default ones.
Rising the price is a difficult thing as well. There is a border, which I like to call "The line of emptiness", which occurs somewhere between 15 and 25% over default, up to competition, when your LFs drop significantly. BUT this can also happen at just 5% above default, if competition is strong. This is why it is difficult to rise as well.
Just keep it default, always the safest
you won't lose money due to too cheap tickets, and won't lose passengers due to too high fees.