There are a few things you should not do when cleaning your laser optics. Do not use paper towels, as the rough fibers in them will actually damage your optics and create minute scratches on your lens. You may not be able to see the scratches, but once you magnify you can understand why the laser beam does not freely pass through and hence reduce your laser efficiency. You should never use a rag or cloth, which could contain particles and could also scratch your lens. Another product that I would not recommend using is the traditional Q-tip. Once again, you run the risk of scratching the lens with Q-tips.
I recommend using proper laser optic tissues when cleaning the lens. These are inexpensive and available from numerous sources including laser manufacturers. These are handy in those tight spots.
Depending on your laser, you may have to remove the lens and the accompanying holder to clean the lens. After this, you simply spray off any debris from the optics using compressed air. Second, you need to apply the cleaning solution to the optics by spraying it on. Last, using light pressure, use the laser tissue or special Q-tip to remove the grime from the lens. Ensure that you clean in one direction and do not re-use the same spot of the tissue or Q-tip. It goes without saying that you should never wipe the laser optics with a dry tissue or traditional Q-tip. Always wet the optics and the tissue when you are cleaning.