Hire the Right People - Support people need several key skills, including being good communicators and having good technical skills, but more importantly, they need to be good, logical troublshooters.

Build Support Infrastructure - Don't neglect the proper support infrastructure, such as phone systems with ACD, email aliases, call tracking and escalation, and having dedicated support hardware for reproducing problems.

Integrating with QA (pre & post release) - A key use of support resources is to integrate with the QA organization to assist in product testing.  In addition, the support group will be feeding bug reports directly to QA over the lifetime of a product, so a good working relationship is key to success.