Just remeber D'AMICO. Sure it's an italian last name but according to Oracle ILT materieal you tune in order.
Design (usually too late for this one)
Application (SQL apps)
Memory (SGA, ect..)
In & Out
Contention
Operating System

I also reccomend the oracle press Performance Tuning book bt Richard Niemiec.

[url]http://www.bookpool.com[/url]

Good Luck MH