You should buy a good lens cleaning kit: a Blower, Lens Cleaning Paper, and lens cleaning fluid.
A larger kit here:
Giottos Rocket-Air Blower Large Cleaning Kit & Lens Pen | eBay
I would not use the same cloth that you use for your glasses: they tend to pickup too much oil and grit.
With the lens cleaning paper: good for one cleaning, next one is clean.