I'll try to cover all major performance aspects of a drupal website; Including front-end but focused on back-end.

The main topics are:

Basic performance settings. Aggregate JS/CSS to decrease http requests number. Compression.
Choosing modules / Avoid redundant functionality. (why install Context if we have Blocks and Panels)
Known performance issues (views contextual filter validation, node access modules...)
Optimizing content structures. Performance impact.
Caching:
- describing and comparing cache backends
- cache services setup and configuration (memcached, varnish)
- caching strategy
- block caching and node access modules