Locking down a linux machine is getting easier by the day. Recent advancements in systemd-boot have enabled a host of features to help users ensure that their machines have not been tampered with. This guide provides a walkthrough of how to turn on many of these features during installation, as well as reasoning for why certain features help improve security.
The steps laid out below draw on a wide variety of existing resources, and in places I'll point to them rather than attempt to regurgitate full explanations of the various security components. The most significant one, which I highly encourage everyone to read, is Rod Smith's site about secure boot, which is the most comprehensive and cogent explanation of UEFI, boot managers and boot loaders, and secure boot. Another incredibly useful resources is Safeboot, which encapsulates many of the setup steps below in a Debian application.