Generally most places use clean water and detergent to clean bare optics. Lens cleaning fluid is highly detergentized water and can be used sparingly (you don't want to get it into the lens set so there isn't much used) followed by a distilled water (the cleanest water available) rinse of the lens.
Don't rub the optical surface with any pressure or you can get scratches. There is a technique that will work with clan optical surfaces where you pull a towel across the surface and allow the beading of the glass to keep the water from sheeting across the surface.
These are the right techniques to use.
Please note that somebody washing a window uses a wholy different technique than somebody cleaning a 1/100th wave accurate optical surface. In addition, using materials that don't scratch glass helps as you are more sure that the surface won't be affected permanently by the cleaning.