One very useful tool is the Lens Pen, sold for $10 to $15 by many mail order supply companies and also many professional photo shops. It has a sable brush on one end to gently brush off dust, and on the other end is a soft cleaning device embedded with a non-liquid cleaning solution. I've used it on my eyepieces (we're talking $250 to $400 eyepieces here)with good results. If the eyepiece in question is one with very small lenses (say, a 6mm Plossl) there's a "mini Lens Pen."
Another approach--one that makes me shudder but that has been recommended by Al Nagler, the world's best eyepiece designer--is to use clear rubbing alcohol and clean Q-tips, with just a small amount of liquid visible on the lens and very little actual pressure applied. One makes an outward spiral, with the hint of alcohol following the Q-tip by surface tension. Don't let any excess liquid pool at the edge of the lens, or it will find its way inside and fog your lens. It will take forever to evaporate.
One of my friends uses a spray bottle of alcohol, holding the eyepiece upside down, and just sprays. I worry about too much liquid for the reason just mentioned, but he says that holding the lens upside down avoids this.

• Ether - chrisdeceu - August 19, 2003 - 06:15 UTC
• Lenses - man5375 - April 9, 2005 - 16:44 UTC