Once you acknowledge you pick up on other peoples emotions so easily and that it's a gift, not a curse, it's easier to detach *your* feelings from *their* feelings. You don't need to "shield", you can just realize that those are *their* feelings and kind of "push" them away from you.
The hardest part is learning how to separate the feelings, but if you get in a habit of checking your own feelings thoughout the day, it becomes obvious when someone else's emotions are "bleeding through."