The most important thing to keep in mind about performance tuning is: Be sure you're tuning what needs it.

I've seen months and fortunes wasted tuning things that nobody cared about except the person doing the work.

Be sure you tune based on RoI and actual business-needs, not just on "this DMV tells me that this query takes a long time".

After that, I've found tools like Ignite very useful for identifying problem queries and priorities.