Dread is a hard emotion to pull off in a roleplaying game though you'll have an easier time of it than trying to pull off a Cat Scare in a storytelling medium (unless you're good at making sudden loud noises). The trouble is that dread is also a discouraging emotion. It's that feeling you get when you don't want to take a step further. That sensation that whatever you'll find behind the door is really not what you want to find. Some people revel in that sense of dread, loving the anticipation of something wicked about to happen, but even so, consistent and long-lasting dread is actually quite draining.
So how do you evoke it?
Basically, find ways to convince your player characters (and hopefully your players) that something terrible is about to happen and slowly build up to it. Use plenty of foreshadowing. Keep them guessing. Generally, once they know what they're up against they can steel their resolve against it or react emotionally to it and that may lead to fear, sorrow, anger, or simple dedication. You can't really control which, though you may be able to predict it.
Keep them hanging on to your every word like the next hint might just clue them in to just what they'll face. Make sure most of the clues are a 'bad sign' and try to start off with clues that are ambiguous. "Oh, the front door to my house is open, maybe my wife is home?" And slowly build up to more nasty seeming ones. "Is that blood spatter on the ground? Did she get a blood nose?" Be aware, though, that once they find the corpse the tension is blown as the player character now reacts (unless you also seed in hints that they're not alone in the house and the killer might still be here).
Be aware that if the players can predict you, that if its a foregone conclusion that there's always going to be a worst case scenario like a corpse, then the dread vanishes as the players now know what to expect and will be starting to build a plan in their minds. This will allow you to build up other emotions, potentially, but we're not covering other emotions just yet. Just dread.
So play up the unexpected. The blood spatter is because the wife got startled by a noise and cut herself while chopping the carrots and when she went outside to take a look she noticed that something had burrowed a rather large hole in the back yard. She hasn't gone down there to look just yet but she's planning to because she thinks that the neighbour's kid has gone down there.
Or perhaps it's there because they were robbed and his wife was injured but is otherwise safe. Not everything has to end in death.
Just be sure that when you raise the dread there's generally a negative outcome at the end. Very occasionally it's okay to have it be a prank or a surprise birthday party but don't make too much of a habit of it. It's good if the players assume that something terrible will happen. That'll raise the tension.
Whether it's a single session adventure, a multi-session adventure, or a campaign, it's important to have 'brake pads' to the dread and action sequences. These 'brake pads' should vary in size depending on the length and needs of the game. Basically, they're calm and safe moments that diffuse the tension, allow a rest, and help people get back into the swing things. This is important both because dread is draining AND because humans habituate to constant stimuli. Just as you'll stop smelling that funky stench if you're stuck in a room with it for hours, so will you get used to dread, or just get over it. So give them funny moments. Give them safe moments.
You don't have to puncture the dread entirely with something wacky. It often works better to keep it low-key. Dry humor. A safe light-filled bar where they can steal a few hours before heading out into the darkness to face those light-sensitive beasties. An interesting NPC that steals the show for a short while. Things that inspire other emotions - and incidentally also inspire attachment, which ramps up the tension later on.
So there you have it. My tips on dread. Do you have any of your own?
See the rest of the articles in this series over here!