Another variation is to make two individual decreases in the center. This means casting on an equal number of stitches and in the center four decrease thus: k2tog, k2tog through the back loop. Depending on which way your stitches are facing you made need to slip 2 and rearrange them on the needle before knitting them together so they face the right direction. This is easier than it sounds. No matter what you do, be consistent and it will look good.
This variation is k2tog, sl1, k2tog through back loop. On the wrong side you must remember to purl the slipped stitch to keep it looking correct on the right side.
Here is where I knit the center instead of slipping it. Still it works. I am not concerned enough to unknit it, since the shape still comes out the same. You will note that I have a garter ridge every fourth row, and kept that pretty consistent over the entire garment.
Here is a diamond which is a center double decrease on every row, both right side and wrong side. Garter stitch throughout. This is something I haven't used in a garment yet, but it will appear in a vest in the very near future.