For a formal, having everything work together is key.
Depending on your dress color and length, always make sure the color palette you select for eyeshadows, blushes and lip products, etc., are balanced with the outfit selection.
If you're wearing a cool-toned dress/outfit (cooler blues, purples, blacks, whites, silvers, reds, etc.), and if you have pale eyes (light brown, blue, green, grey) wear plum and warm brown for eye shadow, and keep the rest of the face bright and fresh. Darker eyes (browns and hazels) will work for this look as well. Plums and browns complement all eye colors, whereas with paler eyes, the eyes are more piercing.
Take a flesh toned color and place it all over the lid to absorb oils that form on the eyelid, especially after putting on eye primer.
Apply a light matte brown and apply it to the crease. Apply a lavender on the lid up to the crease. Put a dark sparkly brown color on the crease and blend on the edges. Don't overblend, and put your fingers on the end of the brush you're using to blend, so the strokes aren't as rough. 5-7 strokes are enough to blend each color you apply. Place a sparkly plum or a matte plum and place it on the outer v of the eye. Tap the color so you get more pigment. Blend accordingly into the lavender color on the lid. Intense or subtlety is your choice depending on your comfort level. Take the light matte brown from before and put it on the lower lashline. Take the dark sparkly plum color from the outer v and put it halfway into your lower lashline. Make sure its a thin, clean line. Make sure everything is evenly blended so each color is visible and not overblended. Take a shimmery champagne and put it in the inner tearduct. Blend. Put it on the browbone. Blend. Take the light lavender color from before and reapply it to the lid. Take a black or dark brown eyeliner (liquid, gel, pencil, or cream) and line the upper inner rim of the eye. This is optional. Line the upper lashline thin. Put a thick line at the corner of the eye, and use your pinky or cotton swab to smudge. Make the liner as smokey as you want. Put the liner on your water line. Smudge it as you please. apply mascara and/or false lashes.
For the face, keep it bright and fresh. No bronzer, just a rosy blush and a subtle cream highlight on the cheekbone, nose, and cupid's bow. For lips, keep moisturized and apply neutral lip color. Apply clear gloss to center of lips.
If you have a warm toned outfit/dress, do the opposite textures and tones of the colors.
Hope this helps.