Generally you can use a eraser to clean it or use towel with cleanser essence to clean.
If also do not cleanly, you need to specialized cell phone clean store, they have specialized cleaning agent!
I have an IPAQ onto which was attached a screen protector.
Over time I wasn't able to press any icons/sliders etc that were at the edges of the screen so I removed the screen protector which cured the problem.
However I have another problem - A glue like substance on the screen. I cannot scrape it off as this may damage the screen and I've tried a cleaning solution but that won't shift it either.
Has anyone got any suggestions as to get rid of the glue?