1. A method for decoding a video signal, the method comprising: obtaining index information from the video signal, the index information specifying a motion vector candidate to be used as a motion vector predictor of a current block; deriving at least one spatial motion vector candidate from at least one neighboring block satisfying one of selection conditions, the at least one neighboring block being adjacent to the current block; constructing a motion vector candidate group of the current block, the motion vector candidate group comprising a plurality of motion vector candidates including the derived at least one spatial motion vector candidate; assigning a motion vector candidate specified by the index information from among the motion vector candidate group to the motion vector predictor of the current block; and decoding the current block based on the motion vector predictor, wherein the selection conditions include: a first condition that a reference picture list for the at least one neighboring block is different from a reference picture list for the current block and a reference picture of the at least one neighboring block is same as a reference picture of the current block based on picture order count (POC) information.