Step 1: Format of a Message: The solution follows the standard format for a message, including the heading 'MESSAGE', date, time, salutation, the main body, and the sender's name.
Step 2: Content: The message is direct and to the point. It clearly communicates all the necessary information: the occasion (birthday party), the date, the time, and the venue (my house). The tone is friendly and personal.
Step 3: Word Limit: The message is concise and well within the 30-40 word limit.