The 1st TWO digits generally indicate lens manufacturer, except serial numbers starting with 6 or 9, which are single digit lens maker codes
The 3rd digit indicates the year of manufacture. This is a bit confusing, as you have to know which decade a particular style and type of lens was made. 8 as the third digit might mean 1978, or 1988, or even 1998. Hopefully you know enough about your lens to guess its decade.
the 4th and 5th digits indicate the week of the year of manufacture, from 01 to 52
the digits thereafter indicate the manufacturing serial number