Drones are easy; probably one of the very best primers on how that's done well has to be Klaus Schulze's "Cyborg". But then, "Cyborg" also shows how you have to keep a degree of variation in the soundscape to maintain listener interest.
Eno's processes are really different, though. He tends to think more along the lines of interacting systems (probably a lot of his Stafford Beer influence coming thru there) and how to get them to continually output a changing result across time. This is why you have the odd interlocking sequencer parts working how they do in "Discreet Music" and then, of course, the inequal-length tape loops of "Music for Airports". As opposed to Klaus Schulze above, Eno's works of these sorts are just as capable of NOT being listened to actively as otherwise; try this with "Cyborg", though, and the results just sound like your HVAC system is malfunctioning or something similar.