To see it visually when you’re already on the route, you can press the routes button (on the left, with a forked road icon), although if you just want to check the following directions, there is an extremely simple way that has gone quite unnoticed : slide the top bar to the left, which shows you the next exit and moves the map to preview where it is. Here you can see it in action:
Google Maps improved its green top banner a few years ago by making it drop down if we tap on it, but in addition to tapping on it we can also slide it to preview the route. As nowhere is it stated anywhere that this is possible, many people are simply unaware of it unless they have done so unintentionally.
It’s a much faster way to review the next steps in a route without having to swipe like crazy following the path of the blue line. If this helpful little gesture was unknown to you too, now you know.