What's your pointers for running Horror in TTRPGs?

I love a horror game.

First having a system designed for horror will really help you to build tension. As someone else said D&D etc are bad for horror because you're supposed to be powerful, it can work but takes more effort.

Next you need player buy in, everyone needs to want to be a little scared or uncomfortable. You're also very unlikely to get horror movie levels of scared and trigger that fight or flight response as you're all sat round a table playing games together.

Having a good session zero for horror is especially important, to make sure you do it safely, have your lines and veils or your X card available and discuss your boundaries. Some people will be fine with body horror but can't manage anything with children or whatever.

Pacing is key to horror, leave the monster in the dark as long as possible, let the players imagine it and what is going on before you show them with a description. Give them downtime to decompress after a particularly tense moment. Let them make jokes but don't join in during the tense bits, join in during the chill out section.

If your looking for recommendations: Trail of Cthulhu (gumshoe) was great. I ran a SCP style game, just picked a monster and had the PCs try and work out what was happening.

Delta Green is a really easy system to intro new people to, it's d100 roll under and you're playing X-files so people have a strong base to work from. Has some great modules to get you started.

Mothership is wonderful and my current obsession. It's also d100 roll under and it's basically Alien/s in terms of the setting but you could easily fit in whatever you wanted sci-fi wise. The modules that come with the box set are brilliant.

It's easy to inject horror into most settings, my party were really light hearted and jokey in Blades in the dark but I had a few sessions where an automaton was hunting them which they found genuinely scary.

Honourable mention the Fate horror toolkit mostly for the GM advice.

Happy to give thoughts on anything horror related if you've got more questions.