I primarily rely on nyaa (anime) and 1337x (general) as public.
Other then them: TL (easy to get into) and a few others.
My advice: Try to get into private ones.
https://www.invitehawk.com/ and http://torrentinvites.org/forum.php will probably list a few options.
To get into private trackers start with the beginner ones (those are your step stone to get to more "elite" trackers) that may be listed here:
https://www.invitehawk.com/forum/44-open-signups/
http://torrentinvites.org/f37/
Trackers usually open during holidays like x-mas, black friday, eastern, summer or because of specific events like another tracker going down.