A few tips, from my first attempts:
If you go to All and choose sort by Active, Top Hour, or New Comments, you'll find all kinds of weird things. It's a great way to stumble upon communities.
If you see a comment or post by someone who you thought was great, a good idea is to click on their profile, then see what other communities they're active in. It's possible that their interests are also your interests.
Finally, the search function somehow manages to work better than Reddit. Search for stuff!