Castling is a move that you should not overlook when playing chess. Generally it is better to have castled within the first twenty moves in a game. Castling helps protect your king from intruders. Some think of it as actually the king retreating into the castle where he is safe. By castling you do not have to be as concerned about the kings vulnerability. A king is a very poor offensive piece and a king copes poorly with direct attacks. Castling offers the king the protection that he so desperately needs.
Another good reason for castling is that it allows your rook to develop more quickly. Often without castling, it takes a long series of movements to simply develop your rook. Exercise caution though not to move the rook to far away from the protective role it has with the castled king. The downside of castling is that if you attempt to move your rook out for an attack and you have not yet moved any of the three pawns in front of your kind, he can be trapped into a back row checkmate. Always try to have a piece that can go in and block a check if the king is trapped behind the three pawns.
If, after castling, you find that you need to move your protective rook, then it is a good idea to move the pawn that is closest to the edge of the board up one space. This allows an escape route for your king to prevent the back row checkmate after castling. The side that you choose to castle on usually depends more on opportunity than preference. Choose wisely and evaluate the side that seems least vulnerable to your opponent's attacks. Use castling as a defensive method, just does not allow it to trap your king without protective help.