Name of Recipient
The recipients address is not strictly necessary for this type of letter. It can be used, but depends on the circumstances and just how close you are to the person.
Dear (insert first name),
Paragraph 1: Traditionally used to catch up and ask your correspondent how they are, and what is happening in their life. Again, this is not a strict rule, but a guide.
Paragraph 2: This section of the letter should focus on the message of your letter, and this can run for as many paragraphs as you like it to. It’s a casual letter, so this section is entirely up to you.
Paragraph 3: Conclusion. This conclusion need not sum up the rest of the letter in the manner that a business letter might. You might be better served by indicating that you are looking forward to seeing the person, or by giving another personal comment of a similar nature.
Here you can use whatever feels best – Best Wishes, Regards, With Love, etc.