There's many answers to this question. But, to me, it doesn't take long to find samples because my workflow goes like this: I pick 1-3 random LP's and challenge myself to sample whatever sounds there is, and try be creative. I enjoy this method so much.
When I started making beats I was always looking for "the best" samples, and that took a lot of time, more than the beatmaking itself. That actually made the whole beatmaking so boring as the years went by. I ended up having hard-drive full of "dope samples" on which I propably used like 2%..
And since you asked for tips on how to dig samples effectively, i assume you mainly "dig" online? youtube is a great source. If I'm looking for samples online I just search with keywords that point me somewhere (for example: 1974 finnish progressive rock), and If I find an interesting song I see what else the user has uploaded on his channel. Works for me.
sorry for any spelling errors, I just woke up 2 minutes ago.