JIRA Ticket Fields:

Title -> Title
Type (not useful for GitHub)
Status -> Labels
Labels -> Labels
Checklist -> Description
Description -> Description
Attachments (Too complicated to move over)
Issue Links (Only for JIRA)
Comments (in progress)
Assignee -> Assignees
Reporter -> Description
Votes (not useful for GitHub)
Watchers (not possible without better xml data)
Dates (created and last modified)

GitHub Issue Fields:

Title
Description
- Tasklist
Assignees
Labels
Projects
Milestone
Comments
Subscribable

1-1 Conversions:

Title
Description
Labels
- Status can be put here
Assignees
Checklist/Tasklist
Reporter/Creator
- Can't maintain unless everyone migrates their own issues; The original reporter of the JIRA issue is displayed at the top of each new GitHub link
Comments