Simply hold all the strands together and knit on large needles--US size 13 works well for many people--in a garter stitch or stockinette or whatever fairly simple stitch that you love and feel confident using. The more complex the stitch or the pattern, the more challenging it may be, but I have customers using my yarn for entrelac and cables.
I listed this scarf on Etsy, if you'd like to see more details.
If you've never used multistrand yarns before, you will want to practice using two strands on large needles before advancing to more strands or to smaller needles, but virtually all my yarn customers get the hang of it. If you stab the needle through part of the stitch, your mistake will likely go unnoticed because of all the colors and strands involved. And your work can't unravel because the strands you DID stab will hold it all together.
Crochet takes a bit of practice, too. I recommend sticking with the larger hooks.
I have more advice about multistrand knitting in this blog.
Life's an Expedition