How to increase core body temperature long-term?

Need more info: Before any of us can give you a reasonable answer, we need more info. First, why do you want or need to increase your body temperature? What, if any, symptoms is your (apparent) low body temperature causing? Does your medical professional think your body temperature is too low? Typically, what is the range of your body temperature? If you can answer these questions, we MAY be able to help.

No great way: There really isn't a long term way to do this without chemically/hormonally altering your body. Body temperature is regulated by the hypothalamus - a special area of the brain. There is no way to consistently affect the set point in this area. It's why overall temperatures are fairly consistent across people of all different sizes and body types.

Exercise: Anaerobic exercise will increase your Basic Metabolic Rate as you replace fat with muscle and probably your core temperature