Back in the day there was allmusic.com
Man allmusic.com was such an education for me, I browsed it a lot from 2003-2005 or so. My family had DSL so I couldn't listen to previews, I just had to go by what few CDs I had and what I heard on the radio (mostly big beat and trance at the time on local stations) and imagine what a lot of the genres sounded like. Wikipedia was so iffy back then that it served as a really solid canon of music history.
2019 - Spotify and lastfm recs (use the former a lot more now, lastfm was invaluable but its redundant now)
WATMM is pretty damn helpful though other niche forums and subreddits are often good. Blogs 10 years ago were great but most of that excellent niche content is no found via insta accounts or YT uploads.
I don't fuck with soundcloud much but you can easily stumble into great stuff. Speaking of...
Nothing really beats getting into local DIY music either via SC and bandcamp - there's an added dimension when you get into music by people who you can talk to IRL or via email. EKT releases, cassette labels, local record shops. Back in 2013 I took a break from online music recs and dove into undeground cassette labels. It was very liberating.
Tiny Mixtapes, Resident Advisor, Quietus, CoS, are all pretty good. FACT and Red Bull put out great features often.