A significant factor in this is going to be the size of the procurement and whether or not it is more of a project than an administrative exercise. Try and keep any requirements focused on areas that are of direct benefit to you. For the suppliers these will typically include:
certification and acceptance requirements for any materials, equipment and off-the-shelf software;
standards for software development;
standards and methods for project management;
operational standards for security;
operational standards for service delivery, availability and disaster recovery etc.
metrics for services and support.
A good starting point is always the British Standards Institution (www.bsi-global.com/ ...