There are two ways to have earaches from a cold:

A problem directly related to the ear
The middle ear is connected to the back of the nose via the Eustachian tube. This tube drains the ear and allows fresh air into the middle ear. When you have a cold you get swelling in the back of your nose. When there is swelling around the Eustachian tube, a blockage in the ear is common.

This can lead to negative pressure in the middle ear -- it feels like the ear is plugged -- and occasionally can lead to an ache. It can also lead to fluid build-up in the ear, which can be painful. Taking a decongestant can cut down on the swelling in the back of the nose. In theory, this lessens the chance for ear problems.

A problem elsewhere in the head and neck that you feel in your ear
The other source of earaches during colds can be from the throat or swollen glands in the neck. Treating the throat and neck will lead make the earache go away.

Drinking lots of liquids, getting extra rest and taking some pain medication are still the best advice for the common cold. Antiviral medication has not shown benefit to date.