To lose weight, eat a good diet. A good diet does not mean juice fasting, going vegan, or any of the other dangerous and harmful things that are part of many popular diets. A good diet avoids processed foods and includes fruits, vegetables, nuts, meats, eggs, dairy, and other good foods.
Exercise regularly. Exercise increases energy and increases the metabolism. It strengthens the body and grants a myriad of health benefits including stronger bones, an improved memory, and a lowered risk of cardiovascular disease.
Drink plenty of water. This can be 1/2 to 1 gallon of water a day.
Get adequate sleep.
Giving something in return does not mean an offering of food or trinkets. To give back, you can gain publicity for the Demon, work aganst Christianity, work to advance Spiritual Satanism, or any other service you and the God can agree upon. There are many ways to work for the Gods of Hell.