web server improvement

[#1]

We have just setup a web server ( Rehdat 6 , apache 2,0 , PHP , mysql ) , all are standard setting , but no need to do HA , backup & restore is solved. 

I just thinking is there any improvement that I can do to make it run better , in the aspect of security , performance , reliable etc , eg. is there any package that I can install to monitor the security , what security issue that I need to concern ? is there script that I should develop to monitor the performance .. etc 

I am new to web server deployment , could advise what admin task that I should do for a web server ? 

No need provide the detail step to do it , just would like to know what I should do . 

Very thanks