adverb
BAD : Living standards have improved greatly.
GOOD : Living standards have greatly improved.
GOOD : Living standards have improved enormously.
BAD : The children greatly cheered me up.
GOOD : The children cheered me up a lot.
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Greatly is usually placed in front of a main verb, especially in passive structures: 'Your kind offer is greatly appreciated.' 'Stories of panic on Wall Street have been greatly exaggerated.'
To emphasize the meaning of an active verb, use enormously, tremendously or (in informal styles) a lot at the end of the clause: 'In the last forty years education in China has changed enormously.'