how to clean lens?

[qwertyjjj]

I have a few spot marks on the lens of my G12, doesn't seem to affect the photo much but would to clean it, it may be from small raindrops drying.

 

[sactown024]

Lens Pen

Amazon.com: Nikon 7072 Lens Pen Cleaning System: Camera & Photo

 

[KmH]

I can't recommend any lens pen, regardless who makes it. I've routinely seen other people's scratched lenses over the years from them using a lens pen. Debris that will scratch the lens gets embedded in the part of the lens pen opposite the brush.

You'll need a blower, and a natural bristle brush. You can use cosmetics natural bristle brushes (camel hair). I had several 1 inch Delta 1 brand camel hair brushes around.
Giottos AA1900 Rocket Air Blaster Large - Black
Adorama Blower Brush - Large
CAMEL HAIR BRUSH WOOD HANDLE

Get some disposable lens tissue, or lint free cloth:
Tiffen Lens Cleaning Paper Tissue Pack Of 50 Sheets
Promaster OpticClean Professional Lens Tissue - 50 Sheet Booklet

1. - blow any dust off the lens. There may be dust particles smaller than you can see.
2. - gently brush the lens with the brush. Be sure to brush dust from the outer edges of the front lens element including the filter screw threads.
3. - crumple up a lens tissue. Blow a huff of breath (Ha!) on the lens to moisten the surface. Let that soak into the rain drop residue as it evaporates off the lens. Huff the lens a second time and gently wipe from the center of the lens to the edge of the lens. Repeat as often as necessary to remove the rain drop residue.

A huff of breath produces essentially a pure water mist. However, sometimes a cleaning solution is needed to remove greasy residue, like finger prints. get a lens cleaning solution made for camera lenses.
Note that Nikon's lens cleaning kit does not include a Nikon lens pen. Nikon Complete Lens Cleaner Kit