Describing a graph is another task type in IELTS writing task 1. This graph could be a
line graph,
Flickr photo by:
Matthew Simoneau

or a
bar graph.
Flickr photo by:
jimmiehomeschoolmom

In order to give the right description, you need to identify the trends or the patterns in the graph, and then describe them using specific verbs, adjectives and adverbs.
Some of them are:
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Verbs for Upward Trend
increased, rose, went up, peaked, improved, gained, recovered, soared, skyrocketed
Verbs for Downward Trend
fell, dropped, plunged, plummeted, declined, decreased, dwindled,
fluctuated
For Same/Unchanged Trend
levelled off, stabilised/stabilized
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Depending on the rate (speed) of the trend, you may use any of
the following adverbs to describe it.
Big upward/downward trend
sharply, dramatically, suddenly, rapidly, considerably, significantly
example. rose sharply, fell dramatically
Slight upward/downward trend
slightly, slowly, gradually
ex. decreased slightly, increased slowly, gained slightly
Adjectives to describe a trend especially on profits
exponential, huge, big, slight
example: huge decrease/increase, exponential change, slight increase/decrease
Just be sure that the words you use truly reflect the description. Don't use the word skyrocketed, when the change in the data being described is just a fraction or a small one. It just doesn't make sense. Using of the right words says so much of your understanding of the graph or the table.
You must remember as well that in IELTS, it does not matter whether you are using American or British English. Both are accepted.
How do American and British english differ? There is not much difference except in some words.
Think of it this way. In American english, words that has -Z are spelled with -S in British english. Words with -OR become -OUR in British. The ones with -ER are spelled with -RE in British english.
Examples: analyze-analyse, organize-organise, labor-labour, color-colour, theater-theatre
In some cases, they differ in some words, but they mean the same thing.
Examples: elevator-lift, gift-present, refrigerator-fridge, dessert-pudding.
Note: The first words given are American, the second words are British.
You must be consistent in using them. If you are more familiar with the American english, then it must be used consistently throughout.