No secrets. I get recommendations from my friends, I keep track of what musicians/producers/etc. were involved in producing music that I love, and seek out what other works they were involved in, etc. I pay attention to incidental music I come across and pursue it.

I've been doing this for decades and as a result, I have a very eclectic collection that covers almost all genres. This approach may not work for everyone, but it works very well for me.