Looking pretty is often about feeling pretty. However, attending to several aspects of your appearance will make you look more attractive. Behavioral changes will also have an effect on your appearance.
First, start out with good grooming habits. Shower, pluck eyebrows so that they frame the face and keep your hair neat. Shave regularly, and keep your fingernails trimmed and clean.
For makeup, choose flattering colors. Look for eye shadows that complement your eye color: gold and peach for blue eyes, purple or lavender for green eyes and blue or purple for brown eyes. Select a foundation that perfectly matches your skin tone, and apply it in a thin layer. Moisturize the lips before applying lipstick, and always apply under-eye cream to plump the skin. Keep eye makeup subtle for daytime.
For clothing, look for styles that flatter your shape. Likewise, make sure they're clean, pressed and fit you well. If you want to emphasize your eyes, choose colors that either complement or match them.
Next, pay attention to your posture. Stand up straight with your shoulders back, and avoid slouching when sitting. Smile often and genuinely, and look people in the eye.
Finally, while it's not necessary to be a gym rat, fitness will help you look and feel pretty. Find an activity you enjoy, and do it often. Not only will you improve your fitness, your happiness will shine through.