Clicking and accuracy, mainly. Even such mundane tasks such as looting chests have some level of technique involved.
If you're running for a corn chest, and you see a weapon, golden apple or another important item in your chest, put priority on that item and grab it. To be able to do this quickly it takes some practise and good reaction time. If items are closer together, it'll be easier to shift-click them into your inventory. Try to aim for items closer together at first.
When looting chests outside of corn, be wary of other players at all times, even if you saw no-one come your way. Corn is a bit of an action-packed area and so people are in a rush to get items and get out, but outside of corn you can afford to be a little bit less rushed (unless of course someone's probably going to kill you).
Here's a tutorial on how to click faster: