I have, on my developer machine, a SharePoint 2013 with SQL Server 2012(Sp1 + CU6), mainly I focus on BI features.
How to upgrade SharePoint to SP1 and SQL Server to SP2?
Which Service pack should be install first?
It is really doesn't matter which SP you installed First, Rather you have to take the appropriate measure before install the any SP.
For Installing SQL Server SP2, you should shut down the all SharePoint Services so that No connection made to SQL from SharePoint while you updating the SQL Server. We shut down the SharePoint Completely while we applied the SPs on the SQL server 5 months ago.
For SharePoint SP, You should do the following way.
SharePoint 2013 SP1 you can install by executing the Installer. Once completed you need to run the SharePoint 2013 product configuration wizard.