During content Migration , First step to analyze what all data we are going to migrate. Are you migrating from CQ 5.x to AEM 6.x or from other CMS to AEM ?
You can use CRX2Oak tool designed to migrate data between different repositories.
Link:- https://docs.adobe.com/docs/en/aem/6-1/deploy/upgrade/using-crx2oak.html
If your site allows comments, then as reverse replication is not available in 6.1 you have to migrate content to UGC. For it you can use AEM Communities UGC Migration Tool.