Might not cover all of them verbally, but should be in supplementary materials.
setting indentation settings. Changing them per-mode. e.g. c-basic-offset variable. tab-width variable. indent-tabs-mode?
custom-file variable? Storing config made through the customizations system in a different file than init.el?
delete-by-moving-to-trash variable
Backup files. I think the default is FILENAME~, which can be annoying.
global-display-line-numbers-mode
sentence-end-double-space variable
Interactions with system clipboard.
winner-mode?
font configuration
colorscheme