The following is a set of suggestions based on our experience in writing and managing against SLAs.
Keep the agreements simple, measurable and realistic.
This technique creates clarity and keeps the process simpler. Just think of all the hours attorneys will charge to unfold a complex agreement. Being measurable also improves the ability to perform according to the agreement. Realistic goals can be achieved and the penalties can be limited.
Bring business managers and technology managers together during the definition of the customer SLAs.
Map the commitments to KPIs and have these indicators drive the performance metrics of the business units.
By doing so, promises made in the SLA will be able to be met by the underlying technology. The challenge is that the initial SLA should be the basis for internal technology choices, and the underlying technology should help define the limitations of the initial promises in the SLA. This is a "catch 22". The best way to break the catch is to ensure that technology and business managers come together.