None of the recruiters knows in depth knowledge of every job role they recruit for their clients or for their own organization.so it very important to let the recruiters understand your CV very well without difficulty in understanding.
Ex: if you worked as a customer support executive for few years or months in a company and you are applying for a software developer role, then its highly recommended not to add this role in your CV.
Ex: Operating Systems: Windows, Unix, Linux
Languages: VB.Net, C sharp, PHP
Databases: Oracle 10g, mysql.MSSQL