It can be a challenge to master the tension of your yarn when you are learning to crochet. You are not alone as tension is one of the things that most beginning crocheters have a hard time with. Usually, a beginner will use a tension that is either too tight or too loose. The good news is that practice will solve most tension issues, so the first step is practice, practice, practice.
Switch Crochet Hooks
You can also make it easier on yourself by switching crochet hooks if you need to. If you find yourself crocheting too tightly, choose a larger crochet hook. If you find yourself crocheting too loosely, choose a smaller crochet hook. Hooks are not expensive, so it is worthwhile to keep a range of sizes on hand so you can switch if you find yourself working too tight or too loose for any project. The hook size suggested in a pattern might not be right for you at first until you are adept at crocheting.
See How Experienced Crocheters Hold the Hook
Another thing you might find helpful is watching some experienced crocheters to see how they hold their hooks and yarn. Visit a craft store or crochet group to see experienced crocheters in action.
There are a great many free crochet videos online that you can watch. Look for ones that are filmed in such a way that you can clearly see how the crochet instructor holds the hook and tensions the yarn. Everyone has a different way of doing it, so if one person's way doesn't work for you, look for a different example.
A right-handed person would hold the crochet hook in the right hand. Often the right-handed person will use the ring and pinky fingers on the left hand to manipulate the yarn and regulate the tension while crocheting. With the left hand, you also would hold the work-in-progress. In the beginning, the left hand can hold the whole piece. As it grows larger and heavier, the right hand will also help hold it, but they left hand does most of the work.
If you take a look through stitch tutorials, you can see pictures of how a right-handed person holds the hook and yarn:
Help for the Left-Handed
If you're left-handed, you might also be interested in how other left-handed people hold their work. Look for videos and photo tutorials specifically for those who are left-handed. Look for a left-handed crafter to teach you. Your local craft store might know one to refer. Another tactic is to sit opposite of a right-handed crochet teacher and follow those moves in mirror image.
Ask for Help
If you've tried a few different sizes of hooks and practice hasn't cleared up your tension issues, ask a crochet teacher to watch you and offer advice. You might even be able to do live video with a friendly crafter or teacher. You can also frequent an online forum and ask questions.