Planing isn't hard, but it does help that you are clear about what you want to do and why.
Goal: what do you want to achieve, and how will sending a letter or card help achieve that?
Recipient: who does the postcard or letter need to go to. This could be one person, a few people (= a few campaign pages) or a sender's UK Member of Parliament (MP).
Change request: what will the recipient be asked to do (or not do)?Audience: who needs to send the messages to influence the recipient? What appeals to the recipient?
Who pays: sender, organiser or both?
Format: do you wish a postcard (750 character limit + image) or a letter (2 page limit) be sent to the recipient(s)?
Message: Blank, editable or uneditable message? Blank messages result in more unique and personal messages which have a higher impact, but fewer people will send them.
Image: what image do you want to appear on the postcard or in the letter?