If you've never heard of the 3 C's, here's some context.
Basically, it's a strategy for writing issues/tickets that breaks them into the Card (user story), the Conversation (documentation and detailed requirements), and the Confirmation (testing steps and acceptance criteria).
Here's a concise little template that you can copy and paste when creating JIRA tickets.
Note that there's nothing really JIRA-specific about this besides the fact that the headings start with "h2." which is JIRA's formatting. Feel free to steal it and adapt it however you'd like if it's useful to you.