At ProtoTest we believe there are no "best practices" for software QA and testing.  "Best practices" implies that there is one right way to do things - for everyone.   We don't think so; instead we think your approach depends on the context of your business.  Plenty has been written about context-driven software testing, so I won't rehash all that here.  But what do we mean by "context?"  And, what's your context?

For instance - what are the risks you are trying to avoid?  If your software fails (in a big way or a small way), what might happen?  Will a customer abandon a shopping cart?  Will a satellite fall out of orbit?  Will you lose a $1-million a year account?

Also - what sort of development process do you follow?  Waterfall?  RUP? Agile? 

How long have the members of your team been in place - Product and Project managers, developers, testers? Are there risks associated with new members, or a whole new team?

What new, unproven or unfamiliar technologies are being used on the next release of software?

These and plenty of other questions can help to determine your context, and then the appropriate QA and testing practices for your team.