Humans vary in their neurological wiring--some are more visual, some more auditory, some more tactile in their preferred learning mode. This has implications for how they read what we writers write. At root, reading text (rather than listening to someone else read text) requires a complex visual skill that forms images (visual, auditory, tactile, olfactory, emotional) from words on a page or computer screen. Skilled readers, given a sentence such as "He slouched in the chair, glowering at the floor" will picture a sullen-to-angry man whose posture and facial expression show resistance as well as anger, discontent, etc. If it's in a defined historical period, they will put the right clothes on him; if there are others in the room, they will anticipate the reaction of others to this slouching, glowering figure.
The more readers know, the less description they need--and more description than they need can be distracting...even a form of "infodump." For instance, if it's important to the story that it's raining (someone's going to get wet, or fall down on a slick step), describing the rain in detail (assuming it's ordinary rain and not really frogs and newts and umbrellas) and detailing drop by drop what falls,
will leave readers thinking "I know, already--it's raining! Get on with it." If your story is set in London, you don't need to describe Big Ben...or in Paris, you don't need to describe the Eiffel Tower. Readers will have seen photographs.
Even when readers have never seen (or seen a picture of) something, the amount of description you provide should be matched to the use of those details in the story--if they're important to a character, and motivate that character in some way, then even minute detail is fine--but if it's just there to prove the writer has done the research...it's not. (For an example of lush description and detail, look at Kipling's story "My Son's Wife" (it's online here) . Kipling knows exactly how to use vivid detail, but does not go overboard (for overboard, see THIS, scrolling down just a tad.)
Because readers operate in different sensory modalities, it's a good idea to describe scenes using more than one sense. Our technology now allows us to observe vivid images of places and events with visual (and some auditory) input, but it does not provide the full array of sensory input that (for instance) standing in a rain shower does. The temperature of the rain, the intensity of it, the myriad sounds (swishing on tall grass, tinkling as it falls on a tin can, gurgling along in a gutter or ditch,) the smells rain brings out from pavement, grass, trash...all that impacts the character standing in the rain wishing the bus would come. What your character is aware of helps define (and second-order describe) the character...the rain is one means you have of showing how that character's head is wired. So mentioning the fresh green smell (if there's grass) and the sound of drips off the tree your character's trying to shelter under, makes the scene vivid for the reader--and that includes the scene inside the character's head.
A character who's already miserable will notice every discomfort--the cold trickle through his hair, the increasing damp chill of his jacket, a leak in one shoe, the stench of rotting banana peels from the trash can near the bus stop--and be thinking how miserable he is, and how unfair it is that other people are driving past, dry inside their cars, and the bus is late again. A character who's just sold his first novel, or just found a great job, or any other reason to rejoice, will more likely shrug off the discomforts and think of the benefits of the rain, the things he likes about rain, remember good times associated with rain. So he's chilly and wet and the bus is late--nothing's going to spoil the day for this guy.
So the details the writer uses can work on multiple levels: yes, show readers a rainy day that feels rainy, but also show readers how this character reacts to that rainy day.
I personally am not fond of heavy description of characters--certainly not all at once, a half page or page of hair color, eye color, nose length, mouth shape, teeth, skin texture, height, weight, and so on and so on. Physical details of characters, if needed for the plot, should be given, certainly, but it doesn't have to look like a page out of a police report. (Unless, of course, you're using a police report in the story...exceptions abound.) For instance, a character's height can be given in relation to another character, by the point-of-view (POV) character, who notices that someone is taller or shorter, and by how much. (Most of us do not go around thinking "Oh, look, that guy's five-foot-ten-and-a-quarter inches tell"--we think "little taller/shorter than me/someone I know.") Readers need to know someone's hair color (for instance) only if it matters...is part of that person's characterization, or matters to the plot--this is particularly true of minor characters. They don't become vivid and well-rounded by having their hair color given, but by their actions.
Descriptions of actions and places must be vivid enough, clear enough, so a reader can stay oriented in story-space and time--confused readers turn to another book. Describing action sequences clearly is difficult enough, but a full description (what might be needed as stage directions if the story were a play or a movie) can bore readers to the point of tossing the book. I once wrote a story that included a WWI naval battle. From the command point of view, Ship A fires...Ship B fires...Ship A's shells hit Ship A (or don't) and Ship B's shells hit Ship A (or don't), over and over. They also maneuver. I had to work out how fast each could fire (cycle between rounds, on each turret) and thus how many shells A fired, B fired, C fired, D fired, and which direction they turned...but the initial battle sequence was...seriously...boring to anyone but a naval enthusiast. That kind of sequence is for post-combat analysis, not fiction. Shoot, wait, shoot, wait, dodge, shoot, wait...that's not plot, that's just a sequence of actions. Turning that into an interesting and vivid action sequence meant not describing every shot, but instead choosing (from the details I'd worked out) which ones mattered to the protagonist (the admiral commanding Ship A.) The sensory details (sound, smell, sight, the ship's movement) that matter stayed in; the others vanished forever into the bit bin of "delete."
This is the difficult part for some novice writers, who want to put in all the description, whether it's plot-relevant or not. (I did that, too, in my early days and sometimes fall into it even now.) Every description needs to be checked for that relevancy--should work, in most cases, to reveal character and advance the plot, as well as giving the reader a vivid impression of the place/time/situation.