A blanket way to force the MacBook to use less energy is to turn on Low Power mode: Go to System Settings > Battery, or click the Battery icon in the menu bar, and choose Battery Settings. In the On Battery menu, choose Low Power. 

That directs apps to reduce energy usage by slowing or disabling background processes, reducing the screen refresh rate on some models and dipping the display brightness. 

(If you're on a MacBook Pro and the battery is depleting quickly, check to make sure the On battery option is not set to High Power.)

That big beautiful screen uses a lot of energy. You probably don't need to set it to the maximum brightness anyway (1,000 sustained nits is helpful in bright sunlight but not so great for most situations), so drop it to a lower level.

Press the Reduce Brightness button on the keyboard (which doubles as the F1 key on most MacBooks), or open Control Center from the menu and drag the Display brightness slider to the left.

Wireless networking feels like the air we breathe, an essential invisible resource all around us. But it also drains power, particularly Wi-Fi when it's hunting for a network to latch onto. If you don't need to be connected to the internet or Bluetooth accessories like mice or headphones, click the Control Center icon in the menu bar and click the Wi-Fi and Bluetooth icons to turn them off.

Note that clicking once on the Wi-Fi icon just disconnects the current network -- the icon turns white -- but doesn't turn Wi-Fi off. To power down Wi-Fi, click the > button to view available networks and choose Wi-Fi Settings from the menu. There you can toggle the Wi-Fi switch to turn off the Wi-Fi radio.

Some apps demand a lot of processing power, even when they seem to be doing nothing in the background. (Chrome was once a notorious culprit for this, but it has since calmed down.) Low Power mode can help, but it's also efficient to quit power-hungry apps altogether.

To identify overzealous apps, click the Battery icon in the menu bar and see if any apps are listed as Using Significant Energy. You can also open the Activity Monitor app (located in the Utilities folder within the Applications folder), click the Energy button at the top of the screen, and then click the Energy Impact column heading to sort by it. Then switch to the ones you don't need and quit them.

If you're not using any connected peripherals such as external drives or an inserted SD card (on MacBook Pro), Apple recommends disconnecting them. Compact external SSDs (solid state drives) get their power from the computer, and even if they're not mounted, MacOS still expends some energy to keep track of their statuses. Break that connection if you're not using it.

The illumination behind the MacBook keyboards uses low-power LEDs, but every little bit of power matters when you're in the red. Unless you're in the dark and need the key reference, lower or turn off the keyboard backlighting. 

Go to System Settings > Keyboard and drag the Keyboard brightness slider as far left as it will go. If you are in a low-lit room, turn on the option to Adjust keyboard brightness in low light, which will dim the backlighting to minimal levels based on the ambient lighting.

If you find yourself adjusting the brightness frequently, go to System Settings > Control Center and under Keyboard Brightness turn on the Show in Menu Bar or Show in Control Center options for quicker access.

Maybe you're not trying to wrap up work and instead want to ensure there's enough battery power to see how the movie you're watching turns out in the end. It would be just like a scary movie to have your MacBook go black before the climax of the story.

Streaming high-quality HDR (high dynamic range) video looks great but uses more power, so go to System Settings > Battery and click the Options button at the bottom (you may need to scroll to find it). Then turn on Optimize video streaming while on battery.