The 1st rule we've learned is : you look all over the place, not just the kart in front of you.

The 2nd rule we've learned is : no skidding, never. That's really hard to do. But look at top pilots, they don't skid.

The 3d rule is : you do your best time on every single lap (super good pilots do almost the same time on most of their laps, within 0.3 sec range; it's hard to believe they do it, but they do !).

4th rule : figure out the best trajectory. According to my kid's teacher it's a question of 10 centimeters here or there (good luck figuring that out !).

Strangely, passing a car is the last thing you learn. But in retrospect,it's normal : most of the time you run after the one in front of you. The opportunities to pass another pilot are rare (most of the time you're much faster so the blue flags forces them to let you pass).

As a dad, I'd say : find a good teacher, it makes a big difference.