I get it. You have your favorite loop that you know like the back of your hand. You’re the Strava champion of the world. Here’s the harsh truth–no one cares about this except your mom and your doting nephew and chances are they’re even faking it.
If you want to get better, you have to stretch your mental and physical muscles in ways they’re not accustomed to. As long as it doesn’t detract from anyone else’s enjoyment and doesn’t violate the rules of the trails, ride your favorite loop..backwards. You’ll soon figure out that you aren’t as good as a rider as you thought you were, but stick with it and you will be.
Get a good light and some extra battery packs and ride at night as fast as you can without putting yourself in peril. Even the most familiar trails will be a challenge and your bike handling skills will improve automatically. Other ideas–pick a fairly technical trail and ride it as slow as possible without faltering. Pick an easy, lightly trafficked, trail and ride it as fast as possible.