Păi, depinde de subiect. Uite aici planul uneia sub forma de invitație. :)
Dear (your friend's name)
Introduction
(Paragraph 1) reason for writing (present continuous)
Main body
(Paragraph 2-3) your plans for the event, your preparations (going to)
Conclusion
(Paragraph 4) closing remarks
Love,
(your friend's name)
Dacă ai nevoie de altă formă a compunerii, spune-mi. :)