Layering synth leads

I love the Avicii , Alesso ,Calvin Harris, Vicetone etc. LEADS ,they sound huge and really stick in my head.I can come up with a nice midi melody ,the problem is getting the sound like this artists.I know they layer their synths ,the question is, how do they layer them?do they use more than an octave ?how to choose the right sounds?when I layer synths I spend lots of time and I always get a big bunch of sounds on top of each other and not a sound I really like…some examples:
https://www.youtube.com/watch?v=a7SouU3ECpU
https://www.youtube.com/watch?v=yZqmarGShxg
https://www.youtube.com/watch?v=EAxf29WhRS4**

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Hey @houseboy you could try watching these videos that deal specifically with laying leads