Don’t use a double overhand grip, don’t use an alternate grip (AKA mixed grip or switch grip). Use the hook grip, i.e., the grip wherein your thumbs go on the bar first, and your fingers go over your thumbs (Figure 1).
The hook grip video included below goes more in-depth on how and why we hook grip, but suffice to say we use it because, although the Olympic lifts are not as heavy as a deadlift (which certainly requires a modified grip such as a hook or alternate grip), they must be pulled quickly. Because they have to be accelerated, your grip will be compromised if you don’t modify your grip.