I would take time to learn the basics of make-up.
Such as your skin tone. Do you know if you are a pink undertone, or a yellow undertone, a neutral undertone?
Research what eye shadow and other make up is often chosen for your eye color & even hair color. Combine this with research of how different shades pop or blend with your skin tone in making a finale decision. Google image search examples of celebrities, models, ect. with similar features to help get an idea on which colors will look most complimentary.
Secondarily, you must learn where make up is suppose to be positioned.
The standard for eyeshadow is...
(however there are many different types of styles, this is one basic style):
1.Base color goes over the entire upper eye which will be your third lightest shade used.
2. Highlight hue on brow bone (lightest color framing your eyebrow directly underneath your brow)
3. Second lightest color on eyelid (if you were doing a smokey eye, this would not be the case)
4. Darkest shade on the exterior outer corners of the eyes swept inwards into the eye lid creases.. and slightly tracing inward on the bottom of the eye.
5. (Optional) Highlight hue in the inner corners of eyes. On the top of your eyes and a little bit on the bottom of the inner corner of the eye.. such as white or light beige.
6. Use a large brush, sweeping in a circular motion to blend the colors together.
7. (Optional) Use white eyeliner and trace your water line (the pink line inside your bottom eye lid is typically referred to as your "water line" in the make up world) You will probably have to pull down on your cheek with your fingers to expose your waterline in order not to poke yourself in the eye) This is to make your eyes look bigger, by creating the illusion the whites of your eyes are larger.
My verbal instructions may have been very confusing. Luckily there are many youtube makeup tutorial and online eyeshadow & facemake up templates that may be more clear you should definitely check out.
Thirdly you will want to learn where highlighters, bronze, and blush all properly go on your face to bring out your bone structure. This will require learning what your face shape is considered: heart, round, oval, etc:
Again there are templates on the internet that will help assist you with this.
For example, using your highlighter if you sweep it around your temple of your eyes: from the top of your eyes brows, to the side of your eyes, down to your cheeks underneath your eyes in a "C" Shape this can assist in bring out your cheekbones. You also always want to have the area directly under your eyes to be slightly lighter than the rest of your foundation to help make your eyes look more "awake"
Also what helped me was Photoshop actually. I got it in my late teen years and learned enough that I could alter my photos however I wanted. Spending time analyzing my photos with the eye of a graphic artist, adding highlight & lowlights to different areas of my face to improve upon my pictures with the software made me realize what I needed to do differently with my make up. Like when I added more dark/bright pigment directly above my eyelid creases to enhance my eyes w/ photoshop. Just as long as the "power of the computer" doesn't give you unrealistic expectations that lead to frustration, it can also be a useful tool to try on make up looks.
Remember that make-up is a form of art, much like painting and drawing. There are many, many different types of techniques that you have the option of learning and it takes a long time to master and perfect.
I started at 13 and now I am 23. And I still mess up my eyeliner at least 40% of the time. What helps is spending a lot of time learning the basics and the dos and don'ts.
I definitely did some "don'ts" in the beginning. Such as wearing dark lip liner with light pink lipstick! (You don't want to do that). And wearing black eyeshadow despite the fact that is just did not go well with my porcelain skin tone, along with other eyeshadows & lipsticks that were just way too dark.
Good luck. And since you are still a teen, remember to respect whatever your parents wishes are about wearing make-up. Make up isn't ever worth ugly family strife.