Step 1: define what you should measure

Day one in your new job: what should you measure? what is important to the business?

There are 2 approaches that you can combined:

1 - start with a prep work: define the VBF (Vital Business Functions) and then identify services underpinning VBF

2 - utilize the existing Service Level Agreements

Don't underestimate the measurements implementation effort and don't go into too much details. Keep it simple to start with.

Other input sources:

• Service catalogue
• Mission statement
• Department goals and objectives
• Legislative requirements
• Budget cycle
• Balanced scorecard

In small and/or young structures, those inputs may be missing but this should not impair the process per se (it will limit how far you can go thought).
This being said, a complete service catalogue is a must-have / must-build.