The primary goal of the end game is to achieve checkmate against your opponent. There are other goals that must be accomplished in the end game to make this possible though. One of these goals is to develop and centralize the remaining pieces that you posses. Using a rook to control one of the central vertical files is essential since it limits the movements of your opponent's king. Also you may consider moving your own king towards the center of the board since by the end game there are relatively few pieces left on the board to threaten your king. Controlling the center of the board is important throughout the entire game of chess, regardless of what phase of the game you have reached.
When it is possible to do a balanced exchange with rooks you should do so. It does take away your rooks, which are quite powerful, but it also eliminates your opponent's rooks. Eliminating your opponent's rooks will make it much more difficult for your opponent to place you in check. If the opportunity presents itself try to attack a weakness in your opponents position so that your opponent cannot use a piece. An example of this is a pin whereby a piece cannot be moved or else your opponent would be placed in check.
Other goals in the end game include advancing your pawns further down the board to penetrate and weaken your opponent's defenses. The other reason that you want to do this is so that you can ultimately promote a pawn to a queen by reaching the back rank. At the same time look for opportunities to capture more of your opponent's pawns as this continues to weaken their defense and prevents your opponent from promoting a pawn to a queen.