We must consider;
Route
Fuel
Alternates
Weather
Payload
Communication plan
Assignment of Duties
Arrival airport information
Equipment on board
Rostering
Catering
Preparation of aircraft
Aircraft cleanliness
Luggage loading
Aircraft maintenance
NOTAMs
Emergency Drills
Flight Duty Hours;
13 hours
If 3 sectors, then 12.5 hours
If 4 sectors, then 12 hours
If 5 sectors, then 11.5 hours
If 6 or more, then 11 hours
Flight Duty Periods are further reduced when crossing WOCL = Window of Circadian Lows 0200 -> 0559 (a period you require sleep) (even if you extend, you need to remember there is the WOCL)
If a commander extends duty hours, he must given a written report to the operator and a copy has to go to the authority within 28 days.
Minimum rest period = 10 hours (or the preceding number of flight duty periods PREVIOUSLY whichever greater) there should be a clear 8 hours rest period.