Contouring your neck can help to create the illusion of a defined jawline and a slimmer neck. It's a simple technique that can make a big difference in your overall look. Here are the steps to follow for a flawless contouring technique:

1. Start by applying a matte bronzer or contouring powder to the hollows of your neck. To find these hollows, tilt your head back and look in the mirror. The hollows will be the indented areas on either side of your neck. Use a small contouring brush to apply the bronzer or powder, and make sure to blend well to avoid any harsh lines.

2. Next, apply a highlighter to the center of your neck, just above the collarbones. This will help to create the illusion of a slimmer neck and a defined jawline. Highlighting the center of the neck will draw attention to the area and make it appear more defined. Use a blending brush to blend the highlighter into your skin. Be sure to blend well to avoid any harsh lines.

3. Finish by applying your foundation and concealer as usual. This will help to blend the contouring and highlighting into your overall skin tone. It is important to match your contour and highlight shades to your skin tone to avoid any unnatural looking.

It's also important to remember that, when contouring, it's best to use a light hand. You can always add more product, but it's much harder to remove it once it's been applied. And you can always adjust the intensity according to your desired look.

In summary, contouring your neck is a simple technique that can make a big difference in your overall look. By applying bronzer or contouring powder to the hollows of your neck, highlighting the center of your neck, and blending everything well, you can create the illusion of a defined jawline and a slimmer neck. Remember to always use a light hand when contouring and to blend well to avoid any harsh lines. And you can always adjust the intensity according to your desired look.