Formal:
* Cher/Chère: This is the most common and formal way to address someone in a letter. You use "Cher" for a man and "Chère" for a woman.
* Madame/Monsieur: This is even more formal and used for someone you don't know well or someone in a position of authority.
Informal:
* Mon cher/Ma chère: This is a more affectionate way to address someone you know well. You use "Mon cher" for a man and "Ma chère" for a woman.
* Très cher/Très chère: This is even more affectionate and usually used for someone you are close to.
* Cher/Chère + first name: This is a less formal way to address someone you know well.
Examples:
* Cher Monsieur Dupont: (Formal, to a man)
* Chère Madame Martin: (Formal, to a woman)
* Mon cher Jean: (Informal, to a close male friend)
* Ma chère Marie: (Informal, to a close female friend)
* Cher Pierre: (Informal, to a friend)
* Très chère Sophie: (Very affectionate, to a close friend)
Other options:
* A + noun: This is used to address someone by their title or position, for example, "A mon ami" (To my friend) or "A ma sœur" (To my sister).
* Salut/Bonjour/Madame/Monsieur/etc. + last name: This is a more informal way to start a letter.
The best way to choose the right way to say "dear" in French depends on the context and your relationship with the recipient.