How to write a resignation letter
Unless you have no respect for your employer whatsoever it is best to resign to your manager face-to-face and then follow up with a formal letter for the HR files.
The letter should include the date your resignation is effective from, the role you are resigning from and the date of your last day. Refer to the notice provision in your contract or the award that relates to your role. That's it. Done.
A sample resignation letter would read something like:
"Dear (manager's name), I hereby tender my resignation from my role as marketing manager of X,Y,Z company. My resignation is effective
As per my contract, I am providing X,Y,Z with X weeks notice. My last working day will be (fill in the date).
Yours sincerely," Don't forget to date the letter.
Depending on your personal feelings, you might want to add a paragraph or two before signing off. If you have valued your time with the employer, learnt a lot, made friends and enjoyed yourself, say so in just a paragraph or two.
If you have not enjoyed the experience, just keep to formalities. No need to be unprofessional by writing something negative. If your employer holds "exit interviews" you can always off load there but remain business-like.