I'm new to DM'ing as well, so take my advice with a grain of salt. I am decidedly not an expert. With that in mind, I recommend reading Dave Chalker's The 5x5 Method and Mike Shea's The 5x5 Method for Antagonists.
In addition, I recently stumbled on a way to use tables of "random" encounters to respond to and highlight the the actions of the PCs. Some explanation is needed:
The campaign I'm running involves PCs traveling between various areas of a country. I thought it would be fun to have a handful of random encounters and skill challenges prepared that the PCs might encounter while traveling between towns in pursuit of the main story goal. Here are a few examples:
- The group encounters a group of young boys, on the outskirts of some town, who tied a dog to a tree and are throwing rocks at it. Does the group save the dog?
- A local prostitute harasses the fanciest-dressed PC as he passes through town. How does the PC ditch her?
- The locals of Town X can't offer the adventurers fresh water because their well dried up. There are skill checks to enter the well, clear the blockage, escape once the water is flowing again, etc.
My plan was to make a table of my ten or twelve random encounters/skill challenges plus a few "Nothing happens" results and roll for which one to use when the PCs traveled between areas. My intention was for them to be random, but, to my surprise and enjoyment, the PCs' actions and interactions as they traveled made it obvious which encounter or skill challenge to use. For example:
- One of the PCs made a big show of his wealth shortly after arriving in one town. I quickly decided that a prostitute witnessed that exchange and inserted the "prostitute skill challenge" I had prepared.
- In one story-relevant encounter, the group tried to save, intimidate, and glean information from some foe, but one of the PCs killed it, much to the consternation of the others. On their next trip between areas, I introduced the PCs to the "abused dog" skill challenge as an opportunity for the offending PC to redeem himself.
I let the PCs' actions inspire whether and which one of my "random" encounters arised. In some cases, I've taken a basic, between-areas challenge and applied it to a battle where I wouldn't have expected it to work. I continue to add new challenges and encounters to the pool as I think of them.
If you keep these ideas vague enough, they're really adaptable and can be molded to meet almost any situation, planned or not.
For your haunted house campaign, you could create several haunted room scenarios and a variety of stakes, in two tables, to use when the party enters a room. Roll to find out what they encounter and what happens if they succeed/fail. If your experience is like mine, though, the choice of which "random" room to use and which "random" after-effect to apply, will become obvious, dictated by the actions and decisions of the PCs.
Best of luck in creating your campaign.