I'm fighting with amadeus airlines on many routes, winning most of them!! only have a fleet of 46 aircraft!
Anyway, to keep the post on topic, my tip to start AE:
When you first started, before doing anything, take 2x5,000,000 bonds, it will help you get started.
If the used market is empty, take several type of aircraft, the maintenance cost may be huge in the beginning, but it will pays off.
If there are a lot of used aircrafts in the market, lease the oldest one, one type only, build your fleet in this type, my favorite: A320, A330, B777, B747,
If the world just started, deploy one aircraft to several routes, not only one, usually 1x on empty route, maxed on the price, monopoly make money, shouldn't it.
If the world already crowded, get the biggest oldest cheapest VLA from the market, and concentrate on trunk routes.
Last, be flexible to reroute your aircraft if current route doesn't earn you a decent profit.