Spotify suggestions, commercials, and British pop charts (even though I'm American).
Mostly just browsing the new release lists on iTunes and Spotify too. Can't use my friends because even single one of them stopped following music way back in early college; whereas I love to follow the hottest and newest stuff coming out.
Honestly, mostly from an old friend from high school. We have really similar taste, yet he's obsessed with music, is a DJ, and works at a record store, etc, so I mostly just receive benefit from a passive trickle-down situation.
I keep an eye out on pitchfork. If they rate it highly i'll give it a shot, why not?
Otherwise, related artists on google play music (playing a radio station based around an artist usually is pretty solid) and NPR All songs considered and the KEXP song of the day.
I actually just discovered a guy named Alexander Rybak because I was looking up a song called Fairytale, which is also a song by Secret Garden, and I thought there might be another cover of the same song.
Sure there are genres that I prefer but not trying to limit myself to one thing, sometimes I just go into the "New Releases" part of Spotify and start listening from the top and work my way down. I'll do this every couple of weeks or so on and off. I've found things I wouldn't have known I'd liked by randomizing myself a bit.
Music threads on here
Music threads on other forums (usually "what are you listening to?")
Whatever youtube suggests to me on the side column while listening to other music.
What friends suggest, which doesn't happen very often since I'm usually the one telling them about new music.
By listening to everything. Go to a store and hear a song on in the background, hear a song in an ad, something a friend is listening to or just anywhere. Also, going in GAF's Plug.dj : http://plug.dj/pop-gaf/
YouTube and GAF have been the big two for a long time. Now that Spotify's in Canada, I just start a playlist or in the Discover area and I save music I like.
I also have SoundHound handy giving me information on music playing around me that I don't recognize.
I actually started doing a thing back in January, of going to the record store down the street, grabbing a bunch of bargain-bin CDs that I didn't recognize, and giving them a listen. I've been blogging the results as well.
It's been interesting. Some have been total crap, some have been great but just not my style, and a handful hit right on the money. I've even found music that the internet doesn't seem to know exists, which is like maximum hipster.