This stitch is as easy as a double crochet; you’re just pulling through the loops differently. I did the sample in two different colors so you can see the different ways the stitch leans. If you use this for a hat and crochet in the round, the stitch will always lean left and it gives great texture. This sample is made by going back and forth.
Start with a basic chain however long you’d like. In the 3rd chain from the hook, yarn over and insert your hook into the stitch. YO and pull back through the stitch AND the next loop on the hook. YO and pull through ONE loop on the hook, YO, pull through remaining two loops on the hook.
That’s it! I suggest practicing several rows to get used to pulling through the first two loops. If you’ve been doing a lot of double crochet, your hands are going to need to get used to this herringbone stitch.