At first glance, juggling seems like a good metaphor for writing. Since you've got to keep all these things in the air.
At second glance, it is a poor metaphor. For two related reasons; one is that you don't, generally, juggle things that are very different in behavior. Pretty much everything goes up and comes down. But deeper than that, juggling as a skill isn't about running around like mad trying to track the behavior of a bunch of discrete things. It is doing a single carefully-timed operation over and over.
And thus, on third glance, it actually does work fairly well.
Because at the gross level of putting text on page, you need to achieve a good balance of all the things that the text contains. A balance between dialog and action, narration and description. You need to space out the evolutions of the plot rather than have it all solved on one page, the similar evolutions of character, and even (at a finer grain) the steps of each conflict, journey, conversation, fight.
At this reductionist level, you do well to emulate the practiced juggler. Rather than racing madly around trying to prop up various unwieldy things simultaneously, you want to slice everything down into manageable chunks, and move neatly through a practiced cycle of operations.
A chunk of dialog. A chunk of description. A chunk of action. A chunk of internal narrative. Lather, rinse, repeat.
Because, not only do you want a decent balance between the relative weight of all the different elements, you also don't want huge unbroken chunks of any of them. If you have a conversation that's going to stretch over several pages, you break it up with something, with anything; a few paragraphs of description or an internal narrative or even action; something external, something physical, something other than words in mouths.
Even on the sentence level, a big chunk of monolog can (and should) be enlivened with breaks and asides. Bits of "business" are great for this: "And thus we come to the problem of Antarctica," the professor said. He looked down at his pipe, only now seeming to notice it had gone out. He sighed. "Antarctica," he continued. "That land of ice and wind. What we find now is hard to reconcile..."
The same trick works in the middle of a fight scene, or a long bike ride. Invent an observation, an unusual bird to spot, a nursery rhyme that pops into a character's head, a terse phone call. Anything to break up the otherwise possibly indigestible chunk of one kind of thing (be it action or narrative or what).
Never leave any ball in your hand too long; be always aware of the two you've got in the air.
This also links to epicycle theory. The overall shape of a story is one big arc. Introduction, development, climax, resolution. Within it, however, must be smaller arcs. And what keeps things interesting is if these arcs are staggered. So as one problem is resolved, another is just starting to grow serious.
Of course you want to pile up the problems around your climax. One of the absolute great moments of that in my book comes from Star Trek, TOS, "Journey to Babel." Spock's father falls sick, McCoy is just starting a risky operation that puts Spock at jeopardy as well...and Kirk is stabbed by a saboteur and assassin. And then the ship is attacked; so Kirk is up on the bridge grey-faced and wrapped in bandages, the ship is shaking apart, McCoy is swearing as the sickbay shakes and the lights are failing...
As Card puts it, the strongest of these moments is when you link the internal conflict (in Card's opinion, the more important one) with the external. But in any case! The point is that lots of little stories are developing all through the narrative and many of those arcs will conclude.
This includes relationships, discoveries, journeys, all the way down to single arguments or even the punchline of a joke you set up in earlier scenes. So on every page, there's tens of different little epicycles clicking along.
Again, think of juggling. Slice them up into roughly equal pieces and space them out. One major core conflict of the story might show up in every other chunk of text. Another might come to the top every ten. The trick is not so much splitting whatever these arcs are into the obvious thematic segments (Boy meets girl, boy loses girl, boy gives up and joins a monastery) but to a grain size that will let you plop them in at the required interval.
Sure, it helps to have each arc segment end at some natural place. The heroine arrives at the castle. The inventor thinks of using titanium. But it is more important to catch the balls at intervals lest the reader lose track of them completely. You need to open that window on the heroine's journey, even if you have to throw in some artificial mile marker for her: "She thought she could smell the sweet smell of apples already. The castle and its orchards could not be more than a day or two away."