- Use file caching and/or a load balancer and CDN network setup,
- Avoid excessive database (MySQL) queries,
- Optimize your MySQL databases and tables,
- Correct any CSS duplication,
- Consolidate CSS and Javascript files when possible and minimize the code (as opposed to maximized code for editing).
That can shave a few seconds off load times.
Sprites can help but are mostly mental masturbation -- saving milliseconds will not make that much difference.