You'd say, "What visuals and sounds? These are words." But that's the thing -- once you successfully put your readers in a "fictive dream," they're not reading words anymore. They're experiencing the story, and they'll be visualizing the scenes and hearing the sounds. And you want to help them do that with a few literary tricks.
It may not seem apparent, but visual cues can enhance or distract. I'm not only talking about visual descriptions (how something or someone looks). I'm talking about how you make your readers move their mind's eye. Take the following sentence, for example:
Jill's room was a mess: the crooked James Dean posters on the walls, the books on the floor, the holes in the ceiling, the Post-its all over the desk, the torn drapes, the overflowing trash under the desk.
At first glance, there may not be anything wrong with the sentence. But read it again and now try to visualize the scene. What do you think?
Ah ha! Your eyes are moving every each way, all over place. They dart from the walls to the floor, then back to the ceiling and then to to desk, then back to the windows and then back to the floor under the desk. I feel dizzy already.
Now try this instead:
Jill's room was a mess: the holes in the ceiling, the crooked James Dean posters on the walls, the torn drapes, the Post-its all over the desk, the overflowing trash under it, and the books on the floor.
Now there's a good flow. Your eyes seem to sweep through the room as you would in real life, instead of darting all over the place.
This works with people as well:
Jill looks odd with the cigarette in her mouth, her black boots, her platinum hair, and the purple nail polish on her fingers.
Again, our eyes are darting all over her. Instead, try to move more smoothly:
Jill looks odd with her platinum hair, the cigarette in her mouth, the purple nail polish on her fingers, and her black boots.
Sounds are harder to do than visuals. They're more about cadence and rhythm, but sometimes sounds also relate to the visuals. The best way is to read your prose loudly and see how it sounds in your ear. For example, reading the above sentence out loud, it sounds a bit off because the rhythm is off -- it's like listening to a song in which the rhythm is not consistent. The last part ("her black boots") sounds really blunt compared to the rest of the sentence.
Perhaps try something like:
Jill looks odd with her platinum hair, the cigarette in her mouth, the purple nail polish on her fingers, and her shiny, black boots that scream Nazi Germany.
Also, there are words that have sounds to go with their meanings. Use them to create a sensory-rich experience:
Occasionally some birds croak from inside the coppice.
That has a nice ring to it, don't you think?