An updated checklist has been released by Microsoft for high-availability (HA) scenarios in Azure. The intent of the guidance is to help with fundamental infrastructure design to help ensure the components within Azure are resilient. The guide covers VMs, Web Apps and Databases.
For an announcement by InfoQ that provides some context as to why this is important see Microsoft Updates High Availability Guidance for Cloud Apps.
In Azure documentation, the High Availability Checklist is a good reference to review and apply even to existing solutions and the Availability checklist by the Patterns & Practices team is more focused on on design time.