Optimizing and enhancing security of a web application

[Donotalo]

(First of all I would like to say sorry if this forum is not a proper place for posting this thread, as this is not be a typical general/chit chat thread. I could not find a forum to cover all the technologies on which I need help.)

I'm working in a web application. We have release the alpha version today. This is my first real-world project. So as a beginner I'm excited as going through the learning of many things.

Me along with my other two colleagues have been assigned the task of optimizing and building robust security for the whole application. We have been given some online help to start with. I'm also looking for more as I am sure many of you have gone through this situation before and learned many thing. Please post any link on tutorials/tips/tricks/tools that really helped you in real world scenario. We are targeting these:

1) Optimizing database and queries. We used MySQL and InnoDB engine for database and PHP as server side scripting.
2) Enhancing overall security of whole application. We heavily used JavaScript on the client side.
3) Reducing server request and ensuring security.
4) Improving client side performance and implementing better usability.

Thanks in advance.