Get a micro fiber cloth:
Microfiber cloths used to clean lenses are available at electronic and optic stores. They are also used to clean camera lenses. Fold the cloth and keep it in your glass case. They are not very expensive and work well for ages. This kind of cloth is perfect for cleaning lenses. You should never use any paper tissue, towel or any fiber (be it your shirt tail or sleeve) to clean the lens because the grains make an impact and leave scratches. You will probably not notice in the beginning but they will build up with time and one day you will be looking into deep scratches.
Get lens cleaning liquid:
Commercial lens cleaning liquid and sprays are available in optic stores. You can also use vinegar to clean the lens. Warm water with dish bar does the same job very well. Since dish bars are present in nearly every home, they are a popular choice.
Clean with soap water:
Make a soapy solution of the regular dish bar in your home and dip your glasses into it, rubbing them softly with your fingers. The water should be mild warm and not hot. Take out the glasses and drip dry them if they have a water repellant coating over the lens. If they do not, then you have your faithful microfiber cloth to absorb the water on the lens and leave your glasses shining like new.