In order the get band 7 in your IELTS writing, it would be easier for any candidate to achieve band 8 in Task 1 (then you only need band 6 in your Task 2 to get an overall writing score 7).
As it is stated in the IETLS Writing Task 1 band descriptor, you should “present, highlight and illustrate key features/bullet points clearly and appropriately”, which means you have to write a good overview that covers most features (overall change, highest or lowest).
Try to write an overview/summary of the line chart below. (Pay attention to your tenses!)
Here is my sample summary of main feature
It is clear that the figures for petrol/oil, coal and natural gas are expected to increase by 2030, while the new energy fuels (nuclear, solar/wind, and hydropower) are predicted to remain stable. Overall, the consumption levels of petrol and oil are the highest in the chart.