I've always written it in the present tense, so for example, me and my guy are in a wonderful relationship, having the best time, he loves me, etc etc  but it can be anything you want.  Just keep it positive and feel the feeling as you write it and imagine it.  Use it to create positive feeling energy for you and your person.  You can just re read something you have written or write fresh even if you're repeating aspects of it over and over.  I just think it's a good energetic exercise so I've written much of the same thing over and over.