I have a 2001 ford focus ZTS, how can I upgrade its performance?

my 2001 ford focus ZTS has a 2.0L DOHC Zetec engine and I want to increase its performance, what would you upgrade, install, replace, etc?
Added (1). its a 2001 ford focus ZTS Zetec-E engine if that makes it less confusing.

Read more: I have a 2001 ford focus ZTS, how can I upgrade its performance?