1. Enable all Magento caching layers
  2. Configure your web server to enable Connection Keep-Alive, enable mod_expire, gzip compression.
  3. Enable MySQL Query caching.
  4. Install APC or XCache to cache PHP opcode.
  5. Install Memcache and configure Magento to store session and cache to memory.
  6. Install third-party Full Page Cache Magento extension.
  7. Install Varnish cache server for full page caching on system layer.

Check detailed instruction here: http://www.magentocommerce.com/boards/viewthread/36225/

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