There a number of ways you can do this, each with varying levels of accuracy to the specific year: examining the sleeve for surface wear and tear; checking the sleeve for 'hype stickers' or barcodes; finding the catalog number and searching the Discogs database for specific info; checking the edition of the pressing; checking the center label for telltale signs that it is a first pressing; and examining the dead wax just outside the center label for information about the pressing and the lathe that cut it in the first place.