There is a strategy that is obscenely efficient for this. Spamming very short range, very high xp M planes from ai airlines that have a total round trip time of 1 hour or ideally much less can net absurd amounts of xp and sp. taking LHR as an example, I recently started grinding. My starting point was level 44, as I had stopped playing once I reached intl. I am playing two hours daily, using 60 AI NXs in very close range. In the last two days, or four hours of gameplay, I went from level 44 to level 50. With my 60 NXs I can expect to get more than 20,000 xp and about 100,000 SP just from maxing all of them. Since I am handling each one 3 times per day or more it will take about two weeks to max all contracts. This is more than enough to get regional, and most of the way to intl, from a zero start.