There are many different ways to decrease stitches in your work and they are referred to as 'decreases'.
When decreasing a stitch the way you do it will create a slope in the stitch to either the right or left and you should pick the type of decreases you use to create the end effect you want.
Knit 2 stitches together. This creates a right leaning stitch.
Slip, slip and knit. Slip 2 stitches, one at a time, as if to knit, then knit those 2 stitches together through the back loops. This creates a left leaning stitch.
Slip, slip and purl. Slip 2 stitches, one at a time, as if to knit, then purl those 2 stitches together through the back loops. This is a trickier decrease to work as working 2 purl stitches together through the back loop requires a sharp needle tip.