Ideally you'd gain as much experience as possible and have as much money as possible, whilst not letting people realise how much experience you have, or letting people realise you're being advantaged by money. Whilst being freakishly quick, of course. And having started karting as early as possible, too. Ideally you'd want to be in a go-kart by the age of like, 3.
I wonder whether Vandoorne managed to game the system by accident. No, I don't think he's secretly rich. But thanks to McLaren fiddling their thumbs on him forever, he now has 4 seasons of top level junior racing (1 year of FR3.5, 2 years of GP2, and 1 year of Superformula). Crucially, he'll also be 25 years old by next year's Australian GP. In this day and age, that's OLD! (yes, don't tell me how depressing that is, I'll be 31 by then).
So he's super quick, he started karting aged 6, he's got years of experience on top level junior formula, he's at a much more mature age than most rookies this era, he's been with the F1 team too for years, and he's even had a real Grand Prix in Bahrain this year. And as for money, thanks to McLaren backing, he doesn't have to worry about it as long as he delivers the results. He's essentially the best prepared rookie of ever since they banned free testing, AND hasn't lost any reputation whatsoever. That's remarkable. I don't know who is his manager, but he's either a genius or absurdly lucky.
Now, he's still going to have it extremely tough to be a rookie next to Alonso. Even with all these advantages, you can't seriously put on his shoulders the expectations to beat Alonso outright. But I definitely believe his experience of racing next to him, will be more like Lewis Hamilton's and less like Nelson Piquet Jr's or Romain Grosjean's.