>>95828260 (OP)Horror games require player buy in. If your players do not show up with the INTENTION to be scared, or at least spooked, then its failed before it even started. Explain this to them when you pitch the game, and remind them when it starts.
Don't attempt to do this in an online game. It will just become unserious anyway.
Props, and atmosphere are key. Even if your props are just a burning candle on the table, its better than playing at midday in a brightly lit kitchen.
After all that, its mostly just up to your skills as GM. Descriptions should use a lot of senses, rather than just sight, it helps with immersion. The less stumbling and "umms" you have, the better you can convey the atmosphere.
I'd recommend looking at the Mothership Warden's Operation Manual. Even if you're not playing Mothership itself, the book is more about basics of writing and setting up a horror campaign and its tips are largely setting agnostic. I like Mothership itself as a horror game, but it takes some getting used to as a system.
Oh and do not try and run horror in a system not designed for it, like DnD. It sounds like basic advice, but it some people are retarded and try it anyway.