You may be given a line graph, pie chart or combination of both, a process diagram, or a simple diagram. You will be asked to write a report broadly describing the trends.
You need to remember to give brief introduction about the graph/ chart /process diagram or the diagram. You need to add the timeline details. One sentence describing the broad trend must be said here.
Next para you need to write the trends and details increase /decrease with specific statistics. You need to compare between countries or groups and discuss the trends observed. For a process daigram you just need to write sentences clearly explaing each process.
In the end you need to summarise the whole trend in a line or two and for process diagram you need to summarise the information.