Start with a primer all over this will preserve your look all day. When choosing your eyeshadow colors it is best to stay within same color family or within the same color tone. ( Ex: Color Family: white, silver into black. Color Tones: bright colors or warm colors) If you have dark circles, use a concealer to cover them before you apply eyeshadow or use a under eye collagen treatment.
Your eyeshadow should not extend past the end of your eyebrows it will make your eyes look droopy if it does. Remember to wipe off excess shadow when you are done applying. I also recommend you do your eyeshadow application before your foundation. This way if you make a mess it is easier to clean and will not waste any of your foundation.
Avoid extending the eyeshadow too high. Just go a little above your crease with the dark eyeshadow. Then use a natural matte or sheer color to highlight under your eyebrows.
Make sure that when you apply your eyeshadow, both eyes are even. I recommend applying each color to both eyes at a time, instead of doing one eye completely then the other. This will help you apply the eyeshadow evenly.
I can not stress the importance of blending. You can have the best eyeshadow, most flattering colors, but if they are not blended, it will not look nice. Invest in a soft eyeshadow brush to blend. This will be very worth it. Apply the darker color at the crease then blend like a windshield wiper.Try not to go too high. And if you want the color darker just keep applying at the crease and blending, do not apply it above the crease.
If you are also going to apply eyeliner as well I suggest supporting your elbow with a table. This will give you more stability for a straighter line.