Harbrace Chapter 24 : Subordination and Coordination
Use subordination to relate ideas concisely and effectively.
Use coordination (that is, giving ideas equal structural rank) to give ideas equal emphasis.
24a Use subordination to combine a series of short sentences into longer, more effective units. The idea is to place emphasis on the most important part of the sentence.
Example: I was bored. I went to the movies. I discovered that Johnny Depp makes a funny pirate.
Because I was bored, I went to the movies, where I discovered that Johnny Depp makes a funny pirate.
[Note that those who prefer Hemingway-esque shorter sentences could put a period after movies and start the next sentence with "There I discovered...."]
24a (1), (2), (3) and (4) offer handy tips on subordinating, such as using adjectives and adjective phrases, adverbs and adverb phrases, appositives and contrasting elements, and subordinate clauses.
24b(3) offers and important caveat: Subordinate and coordinate clauses logically. Avoid making faulty connections between two ideas.
FAULTY Chen was only a substitute pitcher, winning half of his games.
BETTER Although Chen was only a substitute pitcher, he won half his games. [Although establishes the relationship between the ideas.]
[Note: This last idea definitely appears in the PSAT and SAT grammar sections, but if you're not on the lookout for it, you can easily miss it.]