How exactly do you track the enemy jungler?

As an ADC main, this gets me killed more often than I would like to admit. I'll think the enemy jungler is top and try to put a little extra pressure on the enemy ADC, then all of a sudden their jungler appears and I'm dead. I'm pretty good about buying control wards as often as possible and keeping tri and river brush warded, but I can never seem to figure out where their jungler is unless he walks over a ward. Meanwhile, I'll be playing with my plat friends and they'll be like "Careful, Lee Sin will be coming from river in 30 seconds" and they're pretty much always right, even if we barely have any wards on the map.