In my experience, not many people are able to write a good overview / summary paragraph under exam conditions. They can see specific information, but they find it difficult to see the "big picture".
Let's try looking for the "big picture" in some data. We can then write a good overview or summary.
Percentage of students able to speak languages other than English:
30% - Spanish
15% - French
10% - German
15% - another language (not Spanish, French or German)
10% - two other languages
20% - no other language
(adapted from Cambridge IELTS book 11)
Writing your overview / summary paragraph:
I'm sure you noticed the biggest number straight away (30% - Spanish), and we could certainly mention this in our overview. Many people then look for the smallest number, but I wouldn't do that in this case. I think there is something better that we can mention: the 80% of students who are able to speak at least one foreign language. Did you notice the 80%?
Here's my 2-sentence overview / summary:
It is noticeable that the vast majority of students are able to speak at least one foreign language, as well as English. We can also see that Spanish is the most widely spoken second language among the surveyed group of students.
PS. I don't usually include numbers in my summary, so I wrote 'vast majority' instead of 80%, and 'most widely spoken second language' instead of 30%. We can add the figures in our "details" paragraphs.