Use everyday language in your letter. Speak as though you are actually having an in-person conversation with the soldier. Use the soldier's name often throughout the letter to grab his attention and make him feel like he's in your presence. Include subjects that you feel will be mutually interesting. For instance, your favorite movie and hobbies are good subjects that could be of mutual interest.
Keep your words and details upbeat and exciting. Use punctuation such as exclamation points and underlined words to emphasis particularly exciting parts of the letter. Add imagery and description to your letter.
Write sincerely. Refrain from using overly complex language and flowery words. Say what you feel in an honest way. Do not overly praise the soldier or flatter him. It makes your letter look less sincere.
Stay positive in your letter. Keep any negativity and complaints to a minimum. Focus on happy subject matters rather than anything melancholy or worrisome.
Include the current events happening at home. You can include news events from the soldier's hometown and news that is on a national level. News is essential in helping a soldier stay connected with his home.