There are two basic methods that I think are the easiest way to get used to the sort of running form you need while trail running.
The first method is to just to get out and do more trail running. The more time that you spend time out there, the more your body is going to learn what it is that you need to do and that you’ll get used to doing it.
The second method, which is especially relevant if you’re a road runner that’s new to trails, is to actually try and practice it while you are on the roads.
Try to count every time that you pick your foot up off of the ground. Instead of concentrating on having a very short footfall you want to just be thinking about lifting your feet up.
Another way that you can do that is by listening for the scuffing of your feet. When you hit the ground, if you’re not lifting your feet enough you might actually hear the bottom of your shoe rubbing against the pavement as you’re running. So just concentrate on just listening and making sure that you have a quiet footfall and that you don’t hear that prolonged scraping of your shoe along the road.