If we are talking SharePoint 2013 and SQL Server 2012 you have the possibility of creating an AlwaysOn cluster for high availability.
I recommend starting with this blog post that will give you a step-by-step guide on how to set it up. Then proceed to read all available articles on TechNet on the subject. This include planning (especially focus on High Availability), install and configure & operate and maintain.
Read all the articles related to SQL before you start planning your approach, weather you need HA and what type of HA (AlwaysOn, Logshipping, Mirroring) and how you want to design your cluster.