Second part of this puzzle is planning to have sufficent fuel. Below tutrorial is very good.
Additonally you can take fuel planning from Simbrief.com, I also use the following to plan for my fuel, which always gives me sufficent fuel without being overladen on landing, no matter the length of flight:
(Distance of Flight / 450 kts) = Min fuel + 10% + 90 mins
example: LAX - JFK = 2598 NM (Distance)
2598 nm/450 kts = 5.77 (5hrs 46mins) = 346.2mins (5.77 x 60 to convert to mins)
346.2 +10% ( 34.62) = 380.82 mins
380.82mins + 90 mins = 470.82 mins
470.82 / 60 (to convert to hours) = 7.847 = 7hrs 51 mins
So load 7hrs 51mins of fuel before push back.