1. disable statistic
2. dont set mysql to innodb

3. avoid cronjob
4. use nginx ( if you preferred apache use nginx proxy )
5. disable clamd
6. avoid hardcode on your script to reduce server load , before upload please use the fix script
7. install opcode code (like : eaccelerator or xcache or APC )
8. use memcache
9. install firewall protection to avoid server attack, ( this for security reasons ) , install APF and try this DDOS Deflate >>>
http://deflate.medialayer.com/10. use minimal OS ,
etc ...