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 affairs.
The main French newspapers are Le Monde, Le Figaro and Libération.
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.