I'll be the oddman out and suggest paying the one-time $20 registration fee for iptorrents.com

It's simple,quick and easy. No need to worry about getting invited/waiting for open signups. Their retention and library is huge. Speeds are also wonderful as a lot of people are seeding from seedboxes.. I'm on most cabal/top private trackers and I still use it more than anything. Been using private trackers for 6-7 years now.

It's got everything you would ever need as it's a "general tracker" so they have games,movies,tv,software etc. If you don't want to pay then checkout: https://opentrackers.org/ for trackers that are having public signups.

myanonamouse.net, a private tracker that focuses on ebooks and audiobooks, is a pretty good place to get started. Registrations are closed, but twice a week they offer interviews to join. The interview is not hard, you just need to be able to answer a short quiz about the rules.

Once you're in it's really easy to maintain your ratios and there is a lot of freeleach content.

I've found audiobooks there that I can't find anywhere else.

Torrentleech recently had open invites in the wake of rarbg shutting down, other sites will sporadically have openings randomly too. When these happen people will sometimes post to places like this to get the news out, but it can be a bit of luck to get in.

Find a tracker that has IRC sign ups. Maintain a good ratio on that account for 6 months and become a power user to gain access to the invite forums