For a SharePoint installation, this page recommends the following best practices and naming conventions for service accounts:

Remember: 
Managed Service accounts are limited to a total of 20 characters - including the Domain Name (for example Domain\SP_Name  - total characters should be less than 20)

Service Account Overview

• SQL_Service, for the SQL Server service.
• SQL_Admin, for the SQL Server administrator.
• SP_Admin, for the SharePoint administrator and setup user.
• SP_Farm, for the SharePoint farm service.
• SP_WebApps, for the user-facing web application app pool.
• SP_ServiceApps, for the service application app pool.
• SP_Crawl, default content access account.
• SP_UserSync, user profile synchronization account.
• SP_EnterpriseAdmin, powerful account for handling all kinds of high privilge operations.
• Farm administrators, normal admin user accounts are used as SharePoint Farm Administrators.

You can also add a "ga" after each Administrator Account to make explicit that this is a "Global Administrator" Account! An example can be "SP_Farmga". So we know that this account is the Global Administrator of the SharePoint Farm.

SQL_Service

​​This account should be used for running SQL Server engine and SQL Server Agent. Create inside Service Manage Accounts Container inside AD to keep it controlled. Have the following characteristics:​

• Belongs to the Users Domain Group.

• ​​Use only for these two SQL services, if installed more (what you should do) keep the service accounts suggested by the installation program..

SP_EnterpriseAdmin

This account is needed for performing high privilege jobs and (such as installing fixes, upgrades, etc.). It needs to have the following permissions:

• Either SQL Administrator or db_owner of all SharePoint databases.
• Local administrator of each SharePoint server.
• Member of Farm Administrators group.

See http://social.technet.microsoft.com/wiki/contents/articles/12438.sharepoint-2013-best-practices.aspx for more information.

Please Note This page is a community driven effort and is open for update. Originally, it was based on the work of Dan Holme (http://www.sharepointpromag.com/author/5052626/DanHolme).