Do not clean the glasses when they are dry. Cleaning the lens while they are dry can leave marks and scratches on the surface, which get worse with time. Lens cleaning solutions are easily available in optics stores for this purpose, but even simple water can do the job. The cloth used to clean the glasses should not be a rough one. Optics stores have microfibre cloths which are very soft and are purpose made. Keep this piece of cloth in the casing of the glasses and use it to clean them frequently to remove dust and marks. In any case do not use your shirt sleeve, jacket or paper towels to clean them.
While commercial eyeglass cleaners do a splendid job, a soap and water solution can also be used to wash and clean glasses. Dip the microfiber cloth in the solution, clean the glasses and rinse them with clean water. Let them dry well before use.
When the glasses are not in use, keep them in a casing. Most eyeglasses come in their own pouches and cases. These are helpful in protecting them from impact and dust collection when not in use. Hardcover cases are better than soft pouches as they provide protection from any falls and crashes. Do not keep the glasses on places like the sofa and bed where there is a greater chances of people sitting down on them and crushing them.
The frames of eyeglasses tend to loosen with every day wear. To prolong their life, tighten them after every few months with a small screwdriver. If you are hesitant to do it, take the eyeglasses to the store you bought them from. They will do the job for you in a professional manner. If loose frames are ignored for long, they will just come off and the glasses will be damaged.