Selection to the AF Academy was a long process, but it starts with getting good grades in high school and working on getting an appointment beginning in one's junior year. Participate in sports, community events, student government, etc. You don't have to do everything, but choose something you like and do it well. You can always stop the process later if you don't want to go, but you can never go back again if you miss a deadline. UPT was hard, and in the beginning it wasn't even fun.
Professional aviation is hard work.
If you accept that going in, you'll have the right attitude. It just won't seem like that at first. Consider UPT as a marathon, not a sprint. You'll feel tired and overwhelmed, but suck it up crybaby, and keep working. The rewards are great.