Surface unit or the oven or broiler element? If it's a surface unit, I'd guess that the either burner socket is worn and requires replacement or perhaps the spade ends of the element are loose or broken. Not a difficult fix in either case - you may be able to use a generic surface unit replacement that you can get a many big-box hardware stores.
If it's the oven or broiler element, you'll likely have to remove the old socket assembly and hard-wire a replacement element in.