Your glasses usually sit really close to your eyes, so the last thing you want is for them to get dirty. You can use a vinegar solution to clean and disinfect your lenses when they're looking a little rough. Combine three parts vinegar and one part water into a spray bottle, and then use that to get your lenses clean. Even if they don't look particularly dirty, it might be a good idea to disinfect them every once and a while.
You can also just mix everything into a small container and use a cloth to apply the solution to your glasses if you don't happen to have a spray bottle on hand.