Step 0: The critical process of measuring progress
The ability to monitor energy usage, and both interior and exterior temperatures, is vital to gauge the effect of upgrades and tweaks. Absolutely critical. If you're not logging your energy and temperature in detail, there's no way to maximize your improvements. A very large part of the efficiency, in all the systems outlined, comes from the post-install setup and refinement. No two installs will be the same, and much of the system configuration will be based on an iterative optimization cycle — continuously refining the system through measured adjustments.
The open source smart home automation platform
Logging hardware and custom code
Microcontroller hardware and custom code