What are the different ways I can open a jar whose lid is stuck and will not open?
1. Using a rubber band or rubber glove - Surround the circumference of the lid with a rubber band and now try to open the lid the same way you would normally do. The rubber band creates additional friction which causes helps open the lid with less force. The same result can be achieved by using rubber glove. 
2. Using hot water - Hold the jar under hot water, the hot water will allow the metal lid to expand allowing you to open the jar. 
3. Using a knife - Break the vacuum seal by poking a hole in the lid using a sharp object such as a knife. Once the vacuum seal is broken, you can twist open the lid with less force.