Binding off in pattern, particularly when the rows preceding the bind off are some form of ribbing, can add stretch to the bound off edge and prevent it from flaring.
To bind off in pattern, you need to be able to read your knitting. Instead of knitting each stitch before passing the previous stitch over it as you would for a standard bind off, you knit or purl each stitch depending on what you did in the row before. This tutorial explains it nicely and demonstrates binding off in 1×1 rib. The explanation starts at 0:46, and the actual demonstration begins at 1:48.