A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Put information familiar to readers at the beginning of a sentence, new information at the end
Revising sentences
Part I. Research and writing: from planning to production

Readers understand a sentence most readily when they grasp its subject easily, and the easiest subject to grasp is not just short and concrete, but familiar. Compare how the second sentence in each of the following passages does or doesn't contribute to a sense of “flow”:

10a. New questions about the nature of the universe have been raised by scientists studying black holes in space. The collapse of a dead star into a point perhaps no larger than a marble creates a black hole. So much matter squeezed into so little volume changes the fabric of space around it in odd ways.

10b. New questions about the nature of the universe have been raised by scientists studying black holes in space. A black hole is created by the collapse of a dead star into a point no larger than a marble. So much matter squeezed into so little volume changes the fabric of space around it in odd ways.

Most readers think (10b) flows better than (10a), partly because the subject of the second sentence, A black hole, is shorter and more concrete than the longer subject of (10a): The collapse of a dead star into a point perhaps no larger than a marble. But (10b) also flows better because the order of its ideas is different.

In (10a), the first words of the second sentence express new information:

10a . . . black holes in space. The collapse of a dead star into a point perhaps no larger than a marble creates . . .

Those words about collapsing stars seem to come out of nowhere. But in (10b), the first words echo the end of the previous sentence:

10b . . . black holes in space. A black hole is created when . . .

Moreover, once we make that change, the end of that second sentence introduces the third more cohesively:

10b . . . the collapse of a dead star into a point no larger than a marble. So much matter compressed into so little volume changes . . .

Contrast (10a); the end of its second sentence doesn't flow into the beginning of the third as smoothly:

10a. The collapse of a dead star into a point perhaps no larger than a marble creates a black hole. So much matter squeezed into so little volume changes the fabric of space around it in odd ways.

That is why readers think that passage (10a) feels choppier than (10b): the end of one sentence does not flow smoothly into the beginning of the next.

The corollary of the old-information-first principle is to put new information last, especially new technical terms. So when you introduce one, put it at the end of its sentence. Compare these:

11a. Calcium blockers can control muscle spasms. Sarcomeres are the small units of muscle fibers in which these drugs work. Two filaments, one thick and one thin, are in each sarcomere. The proteins actin and myosin are contained in the thin filament. When actin and myosin interact, your heart contracts.

11b. Muscle spasms can be controlled with drugs known as calcium blockers. They work in small units of muscle fibers called sarcomeres. Each sarcomere has two filaments, one thick and one thin. The thin filament contains two proteins, actin and myosin. When actin and myosin interact, your heart contracts.

In (11a), the new technical terms are calcium blockers, sarcomeres, filaments, the proteins actin and myosin, but they first appear early in their sentences. In contrast, in (11b), those new terms first appear toward the ends of their sentences. After that, they're old information and so can appear at the beginning of the next sentences.

No principle of writing is more important than this: old before new, familiar information introduces unfamiliar information.