In an interview a TV presenter once said that he preferred reading texts which were "melodious" and balanced. One technique that students can use to make their writing melodious, stylish and graceful is called Parallelism or also parallel structure or parallel construction.
Let's consider the following sentences:
1. The old woman was smart, polite and gave money to the poor.
2. She was beautiful but a spoilt child.
Something is wrong with them, right? - They aren't very easy to read because the rhythm is broken. Now let's change them:
1. The old woman was smart, polite and generous.
2. The child was beautiful but spoilt.
The tone of the second pair of sentences is different - they are easier to read, smoother, more melodious and more balanced.
So parallelism takes place when expressions that are similar in content are similar in function.
Here are some more examples of parallel constructions:
This animated film is full of fun, adventure and comedy.
At night you could hear voices chatting in the darkness and insects buzzing in the tress.
As he worked overtime and because he came up with innovative ideas, they gave him a promotion.
This product is cheap to buy and easy to use.
He spoke slowly and confidently.
I felt that this was just one more in a very long series of fundamentally cheerful, well-ordered, pleasantly uneventful days. ( Bill Bryson)
With life as short as it is, with so many pressing demands on our time, with so many books of information waiting to be read, why should we spend precious time on works of imagination? (L. Perrine, Story and Structure)
On the one hand, they may want schemes and intrigues, mixed identities, disguises, secret letters, hidden passages and similar paraphernalia. On the other hand, they may demand fights by land and sea, dangerous missions, hazardous journeys, hair-breadth escapes. (L. Perrine, Story and Structure)
For exercises on parallelism, go to: http://grammar.about.com/od/grammarexercises/a/completionparallelism.htm