This article came up today on the official WotC D&D website. It's not exactly rocket science, but setting up the ambiance is something that is easily forgotten when you're DMing. You're preoccupied with describing important details, answering questions, or perhaps you're trying to move the game forward to an exciting encounter you have planned. Rather, you should stop as soon as the characters enter a new area and heed the following advice from the article:
I want to put myself, momentarily, into the boots of my adventurers. I want to think about what the air feels like. Is it hot or cold? Dry or humid? What does it smell like here? Are there irritants around? Bugs? Sand in my sandals? And what are the locals—monsters and NPCs—wearing? How do they cope? What impact has this region had on their culture? Their dress? Their mannerisms?
As a player, I can conjure up a pretty imaginitive scene even without the DM describing details. Sometimes I wonder, though, what the scene looks like in the mind of the other players at the table. It's kind of strange to think that all of these characters could be exploring completely different areas in the minds of each individual player. Not that that's a bad thing necessarily, but as a DM I also have a very specific image in my mind and sometimes it's easy to assume that the players have a similar vision. When I DM, I like to present what I've created, but I acknowledge that I don't always do the greatest job of communicating what I'm seeing in my mind. Not only that, but sometimes even the tiniest, seemingly insignificant detail might act as a seed of creativity in the mind of a player, allowing them to conjure up an elaborate rendering of the secondary world within the game.
I also really like the real-world examples that the author used. Having lived in western WA for nearly a year, I can assert that it does feel very different from where I've spent most of my life, in Ohio. Providing a few environmental details of the setting could go a long way in establishing the difference of a particular location compared to the physical region of the players, which many players likely subconsciously project into the game world. I'm reminded of one campaign that I ran years ago in which the main continent that the PCs were adventuring on was in the southern hemisphere of the fictional world. After several sessions, well into the campaign, they were travelling a great distance south and were shocked when I described the weather becoming colder, until they reached their goal which had a climate similar to the northern taiga (boreal forest) of North America. Since I'd designed the world (more extensively than I needed to, I might add, but that was part of the fun for me) it was just a given that the continent that they were on was in the southern hemisphere, but for players which have spent their entire lives in the northern hemisphere it was a jarring experience.
So yes, better to provide too much description than not enough.