There are many option to increase your Drupal site performance. Many of the developers are not following these best practices. Read this below few tip and keep in mind when you develop Drupal projects.
Update core, contributed module and themes:
Always keep the core and contributed module and themes updated. Updates can include bug fixes, performance improvements and additional feature so better update when there is any update. Check your Drupal site updates page to stay up to date. But don't forget to take update before doing any updation.
Install alternative PHP Cache (APC) on your server:
The Alternative PHP Cache (APC) is a free and opcode cache for PHP. APC is a free, open, and robust framework for caching and optimizing PHP intermediate code. APC can offer great performance for Drupal.
Page caching:
When you enable 'Page Caching' the generated HTML store in the cache table. When user open the page this contents load from cache table.
You can enable 'Page Caching' by following 'admin/config/development/performance' path.
Block caching:
Block cache is another method to cache block data same like page cache.
Aggregate and compress CSS files:
This feature will combine multiple module and theme CSS files into one large file. Find the below steps to enable this feature.
Login as your Drupal site administrator.
Go to the Administer > Site configuration > Performance page.
Check the Enabled checkbox for 'Aggregate and compress CSS files'.
Click the Save configuration button.
Use sprite image:
Sprite image includes many small images in single larger image file instead of having many images. The main advantages of CSS sprites that it reduce HTTP Requests.