Since you did ask a 500 point question, I don't want to shortchange you and hopefully the other DBAs here will chime in.
Besides what I said above, here are a couple of pointers.
Physical Oracle tuning. There are 2 BRUTE FORCE, no-brainers:
a) Buy as much memory as possible, and allocate as large an SGA as possible.
b) Buy as fast a disk (RAID10, cache, or solid state disk) and spread the IO out as much as possible
Outside of that, you can get more into partitioning and blocks, optimization of storage, pct used, etc. but before that, I would move to...
Logical Tuning. This is really where the experts excel. Guys who really know how to tune SQL and know the optimizer, and know how to read explain plan very well. I admit I am not as good of a Logical Tuner, but I try to keep learning. Experts like Don Burleson and Ask Tom are constantly putting out articles, I always try to read them. The "black art" of tuning is really 75% on the Logical side, fixing SQL.
8 out of 10 times, when I look at a performance problem on Oracle, they are running million dollar hardware, and have $5 dollar SQL written by a programmer who doesn't know how to write proper group by! So, LEARN SQL, become a pro. Read some of the stuff on here from guys like ststuber, svz, gatorvip and schwertner who really know SQL very well.
Lastly, don't be afraid to keep asking questions. I find that many DBAs are too proud and scared of showing their weakness areas so they won't ask, and so they don't learn, and in our profession, ego is everything, partly because we need to instill confidence in our customers, but we also need to be confident in ourselves. Managing a customer's data that costs millions or billions is not a job for everyone. But, I am not afraid to say "I don't know", rather than give a wrong answer, I'll be darned if I will give an answer just to have something to say. If I don't know what the heck I am talking about. I'd much rather sit and learn from others that know more and watch how they do things, than to be threatened by someone with more knowledge.
