[support] Drupal 7 performance improvement

Dear All I was trying to look t what all steps one need to perform for better Drupal 7 performance. Came across http://friendlymachine.net/posts/2011/5-ways-to-improve-performance-in-drupa.... Almost 5 different ways are mentioned for performance improvement. 1. Druapl cache enabled, css/java script compress 2. Boost module 3. Memcached module + server 4. Varnish cache + server My question is, can one use all 4 of them, or one need to choose only 1 of them. Or one need to choose few of them, can somebody guide me in this regard. Thanks