The grip you use to hold a crochet hook will probably be individualized to what feels comfortable for your hands. It will also likely fall into one of two types of holds – overhand and underhand. An easy way to try these two holds is to pick up the hook as though you are cutting a steak with a knife (overhand) and to pick it up as though you were holding a pencil (underhand).
While there are other methods of holding your hook, I believe these are the most effective. They allow for good control of the yarn’s movement between your hands and give you more stability while trying to maintain tension. I would encourage you to try to learn one of these methods. If it doesn’t work for you, it just doesn’t work and it’s best to move on to something that does.
The most important aspect of holding your hook is to hold it so that you can easily maintain tension of your working yarn. Tension is achieved by the size of the loop on your hook. If the loop is small and tight, the tension of your work will be tight and very dense. To loosen it up, raise the hook to draw the loop upward, while providing slack by lowering the yarn on the index finger of the opposite hand.
Thanks for reading, I hope this helps! Feel free to leave questions or comments!