Reply to Beginner Tips?

Hi, im new to all this DJing malarkey and i recently bought a Numark Mixtrack Pro II. Ive been watching plenty of videos on YouTube of tutorials,live mixes, tips etc like you would expect from a beginner DJ and i was just curious to know if anyone could shed some light onto how DJ's can have buildups from the second track running in the background with the first track building up also so when the first track is about to drop they can switch across to the drop of the second track seamlessly.
I can do it with cue points but i would like to learn how to know when to start playing the next track so that it can blend in at the right point without using cue points. Is it all about just learning the bars of the song?
Any help would be appreciated, Thanks