At best, a cover letter can help you stand out from the pack. At worst, it can make you seem like an uncreative cut-and-paster.
The cover letter or letter of motivation should not repeat the content of your CV nor include banalities. You should also avoid a standard “good for all” letter. Instead, you need to draw the attention of the reader with a personalized and interesting letter which targets a specific company.
This is not mandatory but, if used, should include a clear reference to the advertisement and the position you are applying for (similar to an objective line on a CV).
This paragraph of the letter needs to state who you are, what position you are applying for, and where this position was posted or advertised. In case of a spontaneous application, you also need to mention it in the first paragraph.
This paragraph gives the reasons why you are interested in this position and in the company. You need to show that you have researched the company and have good reasons for wanting to work with them. Be familiar with the profile they are looking for as well as with the missions and tasks linked to the position.
In this paragraph, you need to demonstrate what professional competences or skills you have which would make you an ideal candidate for the position as well as an asset for the company. Don’t overdo it!
Sincerity and a clear, personal tone to describe how your own experiences and skills match the company’s needs will do more than a long impersonal list of all your job activities, which is the purpose of the CV.
The final short paragraph adds the personal qualities you have which will allow you to integrate the team and contribute to the company’s mission. Again, avoid common words, such as “motivated” or “hard worker.” Instead, indicate your motivation and dedication through other, more personalized adjectives or short sentences about who you are.
Add a concluding sentence to thank the reader for considering your application and that you remain available for any further information.
Note that the structure of an Anglophone Cover Letter is slightly different from a Francophone one.