There are a number of factors to consider when setting metrics for your service level agreement. They include the following:
Motivate with metrics. Metrics should motivate both parties to work collaboratively and encourage appropriate behavior
Agree to metrics that are within the control of the service provider.
Choose metrics that can easily be collected and quantified.
Set a proper baseline from which to begin the contract.
Try to agree on a manageable number of metrics. Too many and it will become difficult to oversee.
Ensure all metrics are very clearly defined.