You'd better wash them under warm water.First put your sunglasses under warm running water to rinse the dirt away.Then apply a small amount of mild detergent to your lens and use a soft cotton cloth to gently rub the lenses in a circular motion. Finally rinse them with warm water and let them air dry.
Well, it seems that you are looking for a better way to wash your sunglasses. So, as we can see, sunglasses lenses are quite fragile and they need our attention and protection. So, you could of course wash them with water, and afterwards, you should use silk cloth to wipe out the water, avoid using some coarse burlap to do so, also, you could use some detergent if necessary. Anyway, try to put them in a dry and dark place after using.