Before each and every solar observing session, check the filter’s fit and, if necessary, tape it to prevent slipping.
Never use the filter at the eyepiece (where you look into the telescope), only attach it onto the objective (where light enters the telescope); otherwise it can become dangerously hot inside the instrument – and inside the eyes! In case of binoculars, be sure both objectives are securely covered; with cameras cover the viewfinders front lens!
A filter made of this durable material is relatively resistant to breakage (even during intentional attempts) in comparison with a glass filter. However, care should be taken with sharp pointed objects. Also be aware that the coating can be damaged by scratching or rubbing and take this into account when storing the filter. A filter with damaged foil should be destroyed immediately to avoid accidental use.
Emphasize the importance of caution to those observing with you, especially children. Intentionally removing or damaging to the filter can endanger their eyesight. This is no place for jokes! Never leave the telescope outside unattended during the daytime!
If your telescope has a finder, you should also put a filter on it, or put dust cover on its objective and secure it with tape. Unprotected viewing through the finder would have the same catastrophic consequences as viewing through the main telescope. Additionally, an uncovered finder directed at the sun can produce exceedingly unpleasant scalp burns.
For more Information visit: http://www.transitofvenus.org/june2012/eye-safety