My rule of thumb with description is that it should be enough for the reader to work with but not too much that it crushes their imagination. As a GM, I like to explain what's in a scene that player characters will be able to see and interact with as well as setting the mood or describing things enough that everyone's on a similar page when it comes to imagining what's going on. As was pointed out, sometimes you need to add a bit more detail because context matters. For example, say you describe a man sitting on the street who has a heavy cough. You would probably assume he had a cold or something. If you describe the same man with a heavy cough with open wounds on his face and spittle of blood on his shirt then people are going to react to the situation quite a bit differently. 

Likewise, it doesn't hurt to describe a character's appearance and describe their apparel because it helps the players visualize this person. The thing with roleplaying is it as a creative medium works a bit differently than say reading a book because it's a multi-person endeavor and you have to be able to facilitate each of the player's needs and wants for it to go smoothly. The less you omit in a post, the better, because otherwise everyone else has to fill in the details on their own and can end up with wildly different conclusions from the very limited information presented. 

For instance, let's say you're GMing a game and you say "A ghost enters the room" without context, player 1 envisions a Grim Reaper look alike with hostile intentions and reacts accordingly. However, player 2 imagines a benign lost child who may be able to help and can't understand why player 1 is being a shithead. Player 3, meanwhile, is picturing an intangible white sheet that cannot see the characters and is wandering aimlessly. All the players voice their disagreements in the OOC after they realize all 3 of them had entirely different things in mind when they posted and you as the GM has to spend time rectifying the situation needlessly when an extra sentence or two could have clarified things nicely without causing confusion. 

Hell, I still run into situations where I think I've been very descriptive and covered my bases but still managed to omit something that prompted a player to seek clarification. 

This doesn't mean write a description of food for 7 pages like GRRM or anything because you don't want to bore players to death with needless exposition, but if you provide enough fuel for the fire, it'll sustain itself nicely. Just don't smother it or it'll die and don't skimp out or it won't ever catch.