Step 1: Reduce the number of articles which appear on your front page.
Step 2: Enable caching for your Joomla.
Step 3: Disable/remove all components/modules/plugins you are not using.
Step 4: Enable debugging from the Joomla admin area > Global Configuration and check the number of queries executed. The higher the number, the slower your application will run. If the number of queries exceeds 50, you may consider disabling the extension which is making the most queries.
Step 5: Check your website using this online tool – http://www.websiteoptimization.com/services/analyze/. It will give you valuable information on what modifications can be made in order to improve its performance.
Step 6: Decrease the number of external and internal links on your pages. Leave only the most important ones.