Throw away your eye makeup 6 months after opening.  The applicators used to apply mascara, liner, and shadow are repeatedly exposed to bacteria in the air and on your lashes; after 6 months of everyday use, they can overpower the products' preservatives. 

Liquid products that don't touch the eyes, such as foundation, can be used for up to 2 years; dry face products like powder and lip items are generally formulated to last at least 3 years.