While ticket closure or reception rates are interesting metrics, try researching other common metrics and pick ones that drive the behaviors you want in the department. For instance, reporting the ratio of time spent on reactive vs proactive tasks or direct measures of proactive tasks, such as number of systems with a disaster recovery plan or maximum and average length of time between tests of disaster recovery plans.
This blog post on lessthatdot.com has some well thought out insights on how to help your organization go from reactive IT to proactive IT.
The article does a good job of explaining how Metrics can do a great job of showing where problems exist and improvements can be applied.
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