Frozen spark plugs

["Mike Barron" <jmikebarron@hotmail.com>]

Tried to remove and replace the plugs on the "weenie" a few weeks ago
(TR3) and got two out, and gave up on the other two, and tightened
them back up.   COULD NOT get them out.   Going to try using WD40 to
lubricate the threads by loosening, spraying, tightening and
loosening, and repeating the process until plugs come out.  Question:
How do I prevent this in the future? (Providing I am successful in
getting them out this time)