You’ve already written formal letters in the last few years. Do you do it well? Do you know one of the writing tasks in the final exam is a letter or e-mail? ;)
Just in case, why not visit the following sites?
General tips on how to write a formal letter: layout, rules, content, abbreviations, etc.
Travel plans + seeking employment: samples on how to request information, offering a house exchange, booking a campsite, making enquiries + applying for a job.
Here you have samples of letters related to jobs: resignation, thank you, reference, salary history and cover letters. Here you are another website which is plenty of cover letters.
I hope you finde them helpful!