Teach me/Help me to Tune/Fix Errors on a PHP/MySQL Website hosted on Webmin/Virtualmin

Hosted on a VPS with the Virtualmin/Webmin CP: [login to view URL] receives about 3000 visits a day. My review of the error logs shows the following: [Mon Jul 23 09:10:01 2012] [error] FastCGI process 24288 still did not exit, terminating forcefully [Mon Jul 23 09:10:01 2012] [error] FastCGI process 24193 still did not exit, terminating forcefully [Mon Jul 23 09:10:01 2012] [error] FastCGI process 21554 still did not exit, terminating forcefully [Mon Jul 23 09:10:02 2012] [error] FastCGI process 21646 still did not exit, terminating forcefully [Mon Jul 23 09:10:02 2012] [error] FastCGI process 22264 still did not exit, terminating forcefully Also, I am seeing this error: [Mon Jul 23 09:10:56 2012] [error] server reached MaxClients setting, consider raising the MaxClients setting The goal here is make this website run more smoothly so it efficiently utlizes the resources that it has. The limit on visits should be the number of people who want to visit the site, not problems with the site if its resources are adequate and sufficient. Also, the goal is to teach me, help me understand the process so I could learn and tune/fix errors with a beginners skills other websites that I own using the skills you taught me. I am not looking for an advanced course in PHP/MySQL, just an understaning of what to look for, what it means, and how to fix it.