I started getting 'religious' about AirlineSim about a month ago, and so far have pushed six or so airlines into bankruptcy. I finally figured out the routes I should be flying, but I still have one question. Once you schedule one flight (i.e. ATL to LAX) does that flight automatically return booked, or do I have to create a separate flight number for the return flight?
Thanks all!
Sorry, in addition, why are my flights being automatically cancelled?
Apologies for the “newness” 
Again, thanks all...!
You need a separate flight.
AS pax don’t book return tickets either. They are all flying only one way.
I suggest you read the Airlinesim Bible to more detail (as you are religious :D)! For airlinesim I would recommend this bible written by the holy yukawa. Anyways when doing a schedule you need to consider where the plane goes afterwards, sure you can fly it to LAX but where does it go next? Will you send it back to ATL for another flight or down to San Jose and then to Seattle? The Possibilities are endless but remember that the plane needs to be back at ATL before doing it´s flight to LAX. To keep it clean and effective most of us will fly more flights in a synchronized manner from one airport thereby making it a "hub" which will get connecting passengers. Althoughit isent AS (abbreviation for Airlinesim) related check out this video:
https://www.youtube.com/watch?v=dGXahSnA_oA
Scheduling is really the most basic and logic thing with AS and not that hard and after having scheduled thousands of planes I can tell you it gets very boring. If you still don't understand scheduling I suggest you go and check out real world flight plans online or have a chat with the pilot or even FA of your next flight. Although the Pilots are rarely very aware of a how a is made but they fly where they are told and can give some insight, personally I have had some discussion with pilots about schedule tactics and other things.
Gotta love some Wendover Productions 
Thanks all, especially Matth and CBE. Let's see what happens!
Booking in waves DOES help - big time - after many tries over the years getting a handle on scheduling is a key to success
Right now I am starting and my planes are filling up from my own internal connections so i do not have to rely solely on direct passenger connections
Picking appropriate planes also is very helpful - not too old - not too big - not too slow - but fit for the market you selected and the competition you face.