I'll give you good advice, but it's up to you whether you want to believe it or not. The correct answer is 'one for every file type you care about'.
When I first got into trackers my first inclination was 'get into all of them then find out which ones are good'. That was the wrong approach: there were too many (and I was a shitty member at some), some really hard to get into, and some really insecure. Nowadays I'm on one for HD movies, two for music, none for games (BCG died, Steam won), and one for TV. Of all of these, I already know the TV one dying would annoy me the most, because I can always netflix movies and already downloaded terrabytes of music, but same-night TV torrents are irreplaceable for me. What this mess of a paragraph boils down to: It's a balancing act between what I have and what I want to continue having. There's no value to me chasing a cookbooks tracker, or one for Mac apps (they're all so cheap and with demos ... how many do I really need). Even IF they have great invite forums, the exhaustion from trying to be a 'good member' at a tracker I don't care about is not worth the marginally faster rate at which I get to where I do want to end up.
Once you figure out what you want, the next thing for you to do is to get into the easiest trackers you have access to and be a good member - try to upload torrents, try to make avatars for people, help with coding the website, create fun shitposting threads (and absolutely don't hang out in the 'hot chicks picture threads' because those are a dumpster fire). Do something that adds back to the community. And then wait for someone to notice and invite you to somewhere that might be better, and when they do, consider whether you're already satisfied where you are or something's missing. The hard to get into trackers ARE better, but in very specific ways. BTN is actually great because of its quickness of releases and security (you can always watch game of thrones on Monday from KAT ... but do you want to?). HDBits is great because of the comprehensiveness of its library, but if you never run into the issue of your tastes being too eclectic ... then it doesn't matter. And so on.
OH, also, general trackers are garbage. I keep one active account at one of the better ones literally just in case all my other trackers shut down. I no longer have an account there, but a great website to start at is DigitalHive. It's the most relaxed, easy to be in and maintain an account at general tracker. The staff are nice enough, I'm sure you asking for an invite in their IRC will get you one.