When you start out deadlifting, you'll probably learn to grip with a double overhand grip. This is pretty much the standard. However, as your weight increases, you're going to want something that can grip the barbell a bit better. It really is a matter of preference. There's no magic weight as to when you should switch up your grip (although you'll have people who will tell you there is one). Anyway, the hook grip and the mixed grip may be the better way to grip the deadlift if you're dealing with a heavy deadlift load.
Alright my buff animals, here's 3 grips for deadlifts!
Double Overhand Grip
For the double overhand grip, both palms will be faced toward you. This is the standard, or the default grip. Since there is no magic number in weight as to when you should go onto a mixed ora hooked grip, you need to make that call for yourself. If you start to lose control of your grip and the bar wants to leave your hands when you're lifting, it's probably time to switch up our your grip to mixed or hook.
The mixed grip is when one palm is facing you, and the other is facing away from you. It doesn't matter which palm is facing which way, as long as they are mixed. And you can always switch it up whenever your buff heart desires. The mixed grip provides a more stable grip than the double overhand grip, especially as the weight becomes heavier.
The hook grip is like a double overhand grip -- both palms will be facing you. The difference with this grip is that you'll be trapping your thumb in between the bar and the first couple of fingers. This creates a hook. This hook may feel uncomfortable at first, but over time, you'll get used to it. This grip is also much more efficient than the double overhand grip for heavier weights.