For the most common packs after 1932, dating is fairly easy until 1960.
From 1932 to 1955, a 1" wide DeWitt Clinton Internal Revenue tax stamp was used across the top of the pack. Dating started at 1932 with series 102, and went up to 1955 with the 1" series 125.
From 1956-59, the 3/4" series 125 DeWitt Clinton tax stamp was used.
From 1960-67, there were no federal tax stamps, nor were there any health warnings.
From 1967-70, the "Caution:" health warning was used.
From 1971 to 1985, the "Warning:" health warning was used.
From 1986 to the present, the "SURGEON GENERAL'S WARNING:" health warning is used.
During any of these periods you may find a state tax stamp on the bottom of the pack either in decal or ink form.
Cellophane was not used until the early 1930's, and tear strips were not on cellophane wrappers until about 1936 when Old Gold first started using them.