From where does the numbering of pins of an IC start?

There is always some indication on the IC itself. For example, the standard 14-pin IC (DIP) has a little ';notch'; in one end. With that end ';up'; (pointing away from you) Pin1 is on the upper left corner of the IC. The pins number counterclockwise.





Square chips (PLCC) have one corner beveled (cut at an angle). With the beveled corner on the upper left, Pin 1 is usually on the upper left corner of the chip, and pins number counter clockwise.





Large scale processor IC's use a ';row-and-colum'; designation that is specified by the manufacturer.





But the only REAL way to know for sure is to have a manufacturer's Data Sheet handy. You can usually load these up from the internet.