No matter what system you’re playing, or what your primary gaming interests are (combat, storytelling, characterization, complex plotting, etc.), every campaign can be improved with immersive, you-are-there descriptions of the world and what happens in it.
In my experience, one of the single biggest factors in creating immersive descriptions is including more than just the two most obvious senses (sight and hearing). Smell, touch and (where applicable) taste can be equally powerful as tools to pull your players into the game world.
I’ve always loved crafting detailed descriptions when I GM, and I’ve done this for years — but I didn’t see it as an explicit goal, or actively think about involving multiple senses, before I started writing for Tabletop Adventures. While it takes some effort at first — because it’s so much easier to just describe what the PCs see and hear, and leave it at that — the payoff is worth it.
Vicki Potter, my editor at TTA, has written an excellent free PDF on this topic (direct link to PDF), Using Description to Enhance Your Game. It’s a great introduction to employing all five senses when describing things to your players.
This isn’t the only way to create immersive descriptions, of course. What’s in your GMing toolkit when it comes to immersing your players in the world around their PCs?