Here is the Link to a free trellis yarn necklace pattern, as I have made many times from Lion Brand and also other finer types of trellis yarn, for my Fred Hollows charity crafts stall. See picture of one my attempts below. See below tips for using alternative brands to Lion Brand as Lion Brand Trellis Yarn is now discontinued.
This site has a nice picture of one made. There are other patterns around that are exactly the same but easier to read and better set out but this one has the good photo.