It depends on many factors, such as body type, wrinkles, angles, perspective:
Some tips are; if the subject has a thick body type take photographs at a higher angle ( your camera is higher than their face) this eliminates or rather hides any fat buildups under the chin and under the arms.
Use a longer lens and shoot from about 25 feet to encompass the subject but do not go in close; this eliminates small details such as dark circles under the eyes.
Use diffused light; this avoids harsh shadows and at an angle,never from overhead.
Use a softening filter; this eliminates or hides small imperfections, age spots etc.
If the subject appears to be tense, have them close their eyes, tilt head downwards,take two deep breaths and return to the pose, then take the shot quickly; this relaxes the facial muscles.