Learn the two most basic decreases, K2tog and P2tog.
To K2tog, work to the two stitches to be decreased and then knit the two stitches together as shown. The stitches slant to the right.
To P2tog, purling two stitches together is done in the same manner. This decrease slants the stitches to the right.
This technique is courtesy of Lion Brand Learning Center of Knitting and Crochet Information.