there are several ways to improve your site performance:
1. use higher CPU / better network speed
it would improve your site loading speed, in average, the landing page of your website should be less than 8 sec.
2. improve site loading speed by putting images/videos/flash on the CDN site
using CDN site, the image would not directly load on your website, when user browsers your site, the closest node of the CDN would responsible to provide the web content back to user
3. keep your site alive
keep your site alive is the goal for website owner and for visitors
4. cache your static content
using gzip compression would improve the file transfer speed to the user
5. image caching
if you want to cache the image on your site, please ensure the image you upload are accurate, otherwise it would be cached from the user local computer.
6. SEO for your website
to let your site searchable by search engine, you may need to add keywords, enhance the website structure, etc
7. backlinks
if more people reference your site, it would improve the popularity of your site

you could get help from some of the website below:
web page test
google web master