How can I import "tickets" from JIRA to REDMINE. from a particular project on JIRA to a particular project in REDMINE
You can use something like a Zapier service.
Keep your issue tracking updated with this JIRA-Redmine integration. After you activate this Zap, every time a new JIRA issue is created, a matching issue will also be added to Redmine, providing effortless upkeep for your lists.
This worked for us: http://www.taskadapter.com/
The UI is a bit rough, but at least it can map the fields properly.
Edit: To expand on the answer, it's a utility that moves tasks between issue trackers. I think it works with MS Project as well, although we only used it for JIRA<>Redmine.
In Jira you can export to CSV: https://answers.atlassian.com/questions/84144/how-to-export-issues-as-a-csv-file
There is a PHP based CVS importer for Redmine: https://github.com/juanmf/RedmineIssueImporter
The process doesnt look very straigthforward, but I guess it should be possible.
Also see this issue, which has some older other options for importing from a CSV: https://www.redmine.org/issues/7884
This script mostly works: https://github.com/Kulgar/jira2redmine
Though I had to edit it slightly to account for changes in the Jira XML format.