Many of the top private trackers rely on reputation. Which is why some of them are notoriously hard to get into. They usually also have active mods, admins and forums. They also generally have posting rules for torrents. Anyone wanting to spread malicious torrents would likely get their account banned in short order once it gets reported. not to mention quite a number of them have their own internal release groups that can be trusted.

While it's not impossible, it's far less likely to be an issue on any well run private tracker.

For the most parts, movies and tv shows is generally safe. It's really difficult to do anything from a media file (.mkv/.mp4) and as long as the torrent doesn't contain any other weird files you're fine.

It's with software and games that you really need to be careful. For software, I would recommend m0nkrus releases from rutracker.org . Google translate the comments on any release and you will see whether any release is suspicious.

Games on the other hand is very hard. There are a bunch of really popular sites that will include some sort of crypto software and other questionable stuff along with their games (igg-games comes to mind). The only public space I trust to get games from is fitgirl-repack.site (this domain is the only official one). Other than that, I only trust GazelleGames but you have to find a way into that and I'm not gonna say it's hard but its definitely a bit of effort to join.