Whether it’s for evening gown, swimsuit, or onstage question, the first law of pageant makeup is "more is more." Under hot stage lights, heavier makeup is a must. All the Miss America contestants had to do their own makeup which meant I had to learn quickly. Over the years I've learned that there are multiple ways to do things and different techniques that work for different people.
You just have to experiment and practice to see what works for you, your face, your budget, and your abilities. Like any skill, getting good at doing your makeup is something you have to develop with time and consistency.
You don't need to buy a ton of new makeup, BTW. It seems like makeup companies are always trying to sell us a new eyeshadow palette amirite? When it comes to doing your own makeup for a pageant, you just need to know how to work with what you've got. For instance, layering your foundation twice (letting it dry in between), wearing double sets of eyelashes, and using generous amounts of lipliner are all things that will give you more oomph.