A strong Task 1 response does more than report numbers. You need to understand what the graph shows, select the key features, and organise the information clearly before you start writing.
A weak approach:
“The number of students was 20 in 2010, 25 in 2011, 30 in 2012 and 35 in 2013.”
Simply listing figures does not show which information is important or how the data should be organised.
A stronger approach:
“The graph shows the number of students attending evening courses between 2010 and 2013.”
This provides a clear paraphrase of the question. You can then identify the main trend for your general overview and group related figures together when describing the details.