purepeak has nicely poured light on this. I would like to add something:
While expanding an idea/sentence always try to understand the cetral thought of the sentence given. You may also speak in favour or against the idea but supplement it with logic, arguments and examples. To start with, simply write what actually is the meaning or what the sentence is trying to convey... then take a position and support it with logic, give some examples. For example, if you are given a proverb; 'A stich in time saves nine' you will write its meaning that this proverb actually highlights the importance of time and that we should not put off till tomorrow what we can do today because it may save us a lot of precious time.... Now you may give examples from daily life like a student may perform better if he studies the whole year. But if he starts studying only when exam starts he may fail in the exam... so every thing look good on its time....so on...... In the end, you may again summarize the sentence in different words and thats it..

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