Use highlighters of different colours
Highlighters are good tools to underline the key ideas you will find in the documents of the synthesis. If you use a different colour for each idea, the main points will come out obviously.
Learn link words and logical connectors
Rédiger un texte académique en français is a very good book which will help you to write an academic French text as well as use link words and logical connectors properly.
Use a diagram to work out your key points
As I said previously, reading articles will help you to expand your vocabulary and your knowledge of French current topics.
Courrier International is also a very good newspaper which translates and publishes in French articles from international newspapers. It is a good way to weigh up the pros and cons of international issues.