Here is a list of recently released articles on SharePoint 2013 relevant for planning and upgrade:

  • Hybrid for SharePoint Server 2013
     
    A hybrid SharePoint environment is composed of SharePoint Server, typically deployed on-premises, and Microsoft Office 365 - SharePoint Online. A hybrid environment may be configured to provide one of several levels of integration, depending on the purpose of the integration. Learn about hybrid for SharePoint Server 2013 and Microsoft Office 365 - SharePoint Online.
     
  • Troubleshoot database upgrade issues in SharePoint 2013

    This article includes a list of common issues and describes general principles to help you identify and address upgrade issues. After you identify and address the issues, you can resume upgrade. Learn how to address problems that may occur after you upgrade a database to SharePoint 2013.
     
  • Troubleshoot site collection upgrade issues in SharePoint 2013
     
    When you upgrade a site collection to SharePoint 2013, errors can occasionally occur. This article helps you understand those errors and address them. Learn how to address problems that may occur after you upgrade a site to SharePoint 2013.
     
  • Clean up an environment before an upgrade to SharePoint 2013
     
    Before you start to upgrade from SharePoint 2010 Products to SharePoint 2013, you should make sure that your environment is functioning in a healthy state and that you clean up any content that you do not have to upgrade. You can also take the time to remove or rearrange content so that you will have the structure that you want after you perform the upgrade. Make sure that your environment is in a healthy state, and delete unnecessary items before you upgrade to SharePoint 2013.