I think, this article tells you very basic things that are not so important compared to others so: I will tell you the things you should really check now then what you should do and why and you don't have to read much.
He breaks it down into six major points (with a little explanation for each):
- Benchmark using tools, not just microtime
- Install APC for an easy performance boost
- Caching is good, but your application should perform well without it too
- Log all background processes too (start, end, errors, etc)
- Database indexes are a good thing
- Load testing is a good thing, but planning for a high load is even better