The strength with which oxygen binds to hemoglobin is affected by several factors. These factors shift or reshape the oxyhemoglobin dissociation curve. A  shift to right indicates that the hemoglobin under study has a decreased affinity for oxygen. This makes it more difficult for hemoglobin to bind to oxygen (requiring a higher partial pressure of oxygen to achieve the same oxygen saturation), but it makes it easier for the hemoglobin to release oxygen bound to it. 
The effect of this shift of the curve increases the partial pressure of oxygen in the tissues when it is most needed, such as during exercise, or hemorrhagic shock. 
In contrast, the curve is shifted to the left by the opposite of these conditions. 
This shift indicates that the hemoglobin under study has an increased affinity for oxygen so that hemoglobin binds oxygen more easily, but unloads it more reluctantly.
Left shift of the curve is a sign of hemoglobin's increased affinity for oxygen (e.g. at the lungs). 
Similarly, right shift shows decreased affinity, as would appear with an increase in either body temperature, hydrogen ions, 2,3-bisphosphoglycerate (2,3-BPG) concentration or carbon dioxide concentration.
Note:
* Left shift: higher O affinity
* Right shift: lower O affinity
* fetal hemoglobin has higher O affinity than adult hemoglobin; primarily due to much-reduced affinity to 2,3-bisphosphoglycerate .
The causes of shift to right can be remembered using the mnemonic, "CADET, face Right!" for CO, Acid, 2,3-DPG, Exercise and Temperature. Factors that move the oxygen dissociation curve to the right are those physiological states where tissues need more oxygen. For example, during exercise, muscles have a higher metabolic rate, and consequently need more oxygen, produce more carbon dioxide and lactic acid, and their temperature rises.