It is very difficult to write more complex sentences in IELTS Academic Task 1. However, here are a few structures which you can use to put two pieces of information together. These strategies are excellent when you refer to two actions, where the first action finishes before the second action starts.
EXAMPLES
Car sales rose at the beginning of the period before levelling off and then falling slightly towards the end of the decade in question.
The number of immigrants entering the country rose slightly over the first few years of the period before falling unexpectedly to a negligible level.
After initially falling slightly, the company’s sales experienced a sudden increase from 2002 until the end of the period being discussed.
After reaching a peak in 2012, there was a sharp drop in the number of bus journeys taken.
Having started at a relatively low level, computer sales shot up towards the middle of the period.
Having initially fallen, the number of tourists visiting the country recovered to a point slightly above its original level.
EXPLANATION
We can use ‘before’ with an –ing form of the verb, in the middle of the sentence, to refer to the second or later action
We can use ‘after’ with an –ing form of the verb, at the beginning of the sentence, to refer to the first or earlier action.
We can use ‘having’ with a past participle, at the beginning of the sentence, to refer to the first or earlier action.