I started doing these trims on sweaters and knits some time ago, and find them both useful and quick! You don’t have to worry about finding ribbing for cuffs and collars, and you can also make the neckline tighter if you wish by doing a few decreases in the line. I prefer to use cotton blend yarn if I am trimming cotton/silk or linen knits, and wool yarn for wool, and its a very useful way of using up those end bits of stash.
I first tack/baste a small turn over hem
I then blanket stitch the edge – I normally have about 4-6 stitches per inch but it depends on the crochet hook you will use (I often use a 3mm hook) – in this instance I used embroidery floss (3 strands DMC thread)
and then do a line of (us) single crochet (or uk double crochet) using the top thread of the blanket stitch as the base. If your blanket stitches are very wide, you can do 2 stitches in each. If you are doing a deep neckline band, you could do a decrease (by crocheting 2 stitches together) one fifth in each side and fitting as you go to see if it needs more.
I normally just do a line of (us) single crochet followed by a (us) double crochet, then another line of (us) single crochet and sometimes finish with a picot stitch.
The sample in the photos is a very light jersey, 4 ply cotton yarn, and 3mm hook.