If you decrease at the beginning of the row:
Knit 1 stitch, Knit 2 stitches, lift the first stitch over the second, knit to the end of row.
To decrease at the end of the row:
Knit to last 3 stitches. Knit 2 together, knit one.
Follow these instructions if decreasing on a purl row.
Note the way the different decreasing techniques shape the garment and you can use this to be creative in future!