If I try to answer this myself, I'll probably end up writing a whole book in this little text box and only realize it three hours later. Instead, I'm going to direct you to Limyaael.
Most of her stuff is about fantasy, but this is applicable to basically any genre.
In general, though, your reader should have an idea where the characters are, but shouldn't know about every object in the room, or how the furniture is arranged. Just what's meaningful: the little boy's teddy bear, given to him by his sister, which he carries around everywhere, or the professor's chair by the fire, maybe, because those are prominent things.
But not the side table by the stairs, the potted African violets in the windowsill, and the family pictures on the walls--unless these become important. If there's a dagger hidden in the violets or someone's going to crash into the side table in a fight and you want to mention that it's got a candleholder he can use as a blunt instrument, that makes it important. If the family pictures on the walls include vampires, that could also be important. What's important enough to describe is a matter of your own style, but make sure it's readable. If you can't tell, read other people's novels and compare, and get some readers who are not your family or otherwise sparing of your feelings.
This is sometimes referred to as the Law of Conservation of Detail. Here's the TVTropes page on it. (TVTropes is very useful to writers.)