Matthew Liberty (@mliberty1) shared good advice for lowering power. We talk about different ways to measure current (Matt has a nice write-up) and things software can do to decrease power consumption.
Sleeping is critical, of course, as is choosing your clock speed and setting the GPIOs to good states. Everything is fine until you start getting into the microamps, then your multimeter measurements may start to fail you. (EEvblog explains why in his uCurrent intro.)
Eventually, you may want to measure nanoamp sleep states along with amp-consuming wake states. Matt’s Joulescope is a tool to do just that (Kickstarter goes live Feb 19, 2019!), automatically moving between 9 orders of magnitude of dynamic range and graphing the results on your computer.
Matthew’s consulting company is JetPerch.