Writing a letter to yourself is probably something you had done as a child and never given much thought to as an adult. However, if you look back at the things you had written at the time, it will often appear that there was a glimpse of who you were left behind for you to see. In many ways writing a letter to yourself is like allowing yourself to meet a younger version of yourself when they are older.
When writing a letter to yourself you might choose to leave a concrete message behind for your older self, including a message about how to act or reminders that you do not wish to forget. These young reminders can help inspire more youthfulness and are usually welcomed by readers.
However, if you do not wish to take the advice route there is always the option of using the letter to yourself to recount memories that you do not wish to forget. In some ways, this is like journaling with the only true difference being knowing that you will certainly have someone reading your entry at a later day.
Most importantly when writing a letter to yourself try to make sure that it is simple, sweet, and positive. After all, this is a letter that you will be reading at a later time and you would hate to have to read a pessimistic message that left you feeling deflated. Therefore, be creative and inspiring and leave yourself a message that is worth remembering.