The art of winning.
First off, races are won on the uphill, and not the downhill or flats when it comes to cross country racing.
This is a sport about endurance, stamina and the will to win. Those who ignore pain the best are often rewarded with victory.
The only way you can truly see where you stand as far as your ability is to race. You might be faster and possess more endurance then your friends or those you meet on the trail, but that is just a start point.
If you are serious, sign up as soon as you can for your first race, and begin developing your race craft from your observations of watching other riders in combination with your experience you bring back from the race.
Start here with USA cycling to get in the loop.