Patching SQL Server 2008 and upgrading to 2014
The SQL Server 2014 Upgrade Techincal Guide states that  you need the following as the minimal version for an in-place upgrade


SQL Server 2005: SP4 is required.
SQL Server 2008: SP2 is required.
SQL Server 2008 R2: SP1 is required.
SQL Server 2012: SP1 is required


So if you are not on the stated service pack level you will need to upgrade to at least that.

It is not neccessary, but start by running the upgrade advisor. 
Thomas LaRock has a checklist on his page both for the tasks needed before an inplace upgrade and what to do afterwards.