Wear SPF 30 or higher on your face and neck every day, even when not going outside. You can still get significant sun-damage from driving or sitting by a window.
Avoid smoking- smoking is the 2nd leading cause of pre-mature aging after sun-damage.
Exercise and stay healthy, especially a strong back and core to sit up straight with good posture. If we are slumping with our necks forward those muscles will shorten and the skin will hang more.
Sleep on your back if you can. When we sleep on our sides or stomach often our neck twists and more lines can appear.