I have a bunch of past clients I have not been good at following up with and staying in touch just to say hello. I know how to use campaigns, but i was looking for ideas on what the campaign could be, do you send anything creative, how do you categorize past clients, etc.
Completely up to you what you send as you know your clients, how to connect to them and what the lingo of your industry would be. A content writer can help you to format things in a more responsive way.
‘Categorizing’ clients again, is based on the norms of your industry. However, you can consider those that have responded (opened/clicked) within email over the last 3-6 months engaged while older ones you would want to run through a re-engagement campaign to prevent high opt outs and spam complaints.