Using the Configuration Manager and FMC

Go into your flight 1 menu bar and load up the aircraft config manager. I suggest that you, start off by filling all the seats up in short haul fligh. This should give you 264 passengers. Charter airline passengers are allowed to carry 30 Kgs of luggage. so multiply 264 X 30. This will give you your cargo weight. Distribute your load throughout the different holds so that it works out to about  7920 kilos when added all together

Once this is done note the important things below a

Note the gross weight. if this is above 408000lbs the aircraft is to heavy for take off. If it is above 320000 it will mean the aircraft will be to heavy initially to land back at the departure airport if an emergency develops after take off. The pilot would have to consider dumping fuel or flying around to burn it off.

For rule of thumb fuel calculation for a take off and climb at this ZFW the aircraft in the first hour will burn 13000 lbs this includes climb to FL410

after that allow 10000 lbs per hour. so a 2 hour flight the fuel burn will be 23000 lbs Add 10000 lbs contingency fuel for holding more if weather is bad. So I set the fuel at about 35000lbs for UK to Med destinations. Calculate the aircraft speed over the ground as 430 nm per hour to give you a rough idea of how many hours then add 30 mins.

Now go to your aircraft FMC

cost index between 50 and 200 the higher the more fuel it burns. 80 is about right

Enter your route and departure and arrival airports and activate the route

In this case I have set fuel for a route from Gatwick to Palma a distance of 867 NM