Every phone-based navigation habit falls apart the moment signal drops, unless the maps were downloaded in advance. This is the one lesson worth actually acting on, rather than just nodding along to in a review and forgetting by the next trip.
A downloaded map with no signal beats a live map with one bar, every time — the difference isn't subtle once you've actually needed it.
Download before you leave the car park, not when you notice the signal has already gone. It sounds obvious written down, and it still took me two genuinely stressful moments on a hillside to actually build the habit properly, rather than just agreeing with the advice in principle.
The habit itself takes under a minute: open the app, select the area, confirm the download, and check the tile actually finished before setting off. Most failures I've had weren't from forgetting entirely — they were from starting the download and not waiting for it to complete before losing signal on the drive to the trailhead.
Beyond the download itself, it's worth checking the map actually renders useful detail at the zoom level you'll need on the day — some offline tile sets drop footpath detail that's present online, which only becomes obvious exactly when you need it most and have no way to check the live version.