light depend resistor also type of variable resistor, it has self resistance , any sensor or any electronic device shoul hav some feed, i mean to say powers upply, so connect LDR to Vcc and ground, but it is variable resistance so it may draw power in variable manner, so stablise circuit connect pull up or pull down resistance. i suggest pull down is better to you initially.
pull down configuration: connect LDR point A to Vcc, point B to 10Kohms resistor of one end anotther end of 10K you have to connect to the ground. and connect junction point of both to the A0 pin of Arduino.