Just tell the truth..for the heart speaks a language no words can capture. There is no need for a formula, you write from the heart...it can be as long as you wish or as short as you wish..
In the heart sutra it says:
Therefore the mantra of transcendent knowledge, the mantra of deep insight, the unsurpassed mantra, the incomparable mantra, the mantra which calms all suffering should be known as truth, for there is no deception. In transcendent knowledge the mantra is proclaimed:
GATE GATE PARAGATE PARASAMGATE BODHI SVAHA