There are many things which you can do to improve response time - assuming that you are running a Linux/Apache/MySQL/PHP configuration, I would recommend that you consider the following approach to fine-tuning performance:
1) Optimize your Configuration
You may want to revisit your Apache and MySQL configuration to
optimize for performance and low memory overhead.
2) Find Slow Queries
Isolate
Slow Queries and add index columns where appropriate.
3) Cache Static Content
The fastest way to get data from a database across multiple page requests is to get the data once, write it to disk, and load the
cached data whenever page requests are made.
Depending upon the applications which you are using and your level of programming expertise, this may or may not be easy to implement. Many applications do have caching options built in (check your documentation and ensure that caching options are enabled and configured correctly).
As it appears as though you may be running WordPress, you may be interested in this
WordPress performance discussion, as well.