What must I do to sync my Notes from my iPhone to my iPad and iMac?

Have you set up iCloud on all 3 devices and turned on Notes syncing? On the Mac: Apple Menu > System Preferences > iCloud and put a check mark beside Notes. On the other two, Settings > iCloud and turn Notes on. More info on iCloud setup: http://www.apple.com/icloud/setup/

This looks fine, FoxFifth, but I find I have iCloud enabled and notes syncing on on all 3 devices - but only some notes are synced between iPhone (where I write most of them) and mac mini, and no notes at all appear in Notes on my iPad.