Natural light always corresponds to the current mood. During the day, natural light is usually the right type of light. When it gets dark or even indoors, the light is dim. If you want sharp pictures, you will have to increase the ISO setting quite a lot, which will create image noise in case of a fast exposure. Modern cameras can manage an acceptable image quality at an ISO of up to 2,000. There are even top models that can take pictures at an ISO of up to 10,000 with no noise worth mentioning. You can only see the noise when you enlarge the picture and put it into a photo book, on a mural or a photograph.
At a party, the subjects may be static, such as when sitting at a table. Make sure that the exposure time does not result in slightly blurred images. If you shoot at 1/60 of a second or longer, you run the risk of getting slight blurring – my guideline is 1/250 of a second or shorter. I prefer to shoot with faster exposure times and compensate for this with a higher ISO number. Or I work with a flash. If you use a flash, the light reflected off glasses or windows often causes a problem. If the flash hits the reflective surface at about a 30 degree angle, you have a good chance of having no reflected light in the image (off the glasses). All you need to do is photograph the people slightly from the side, rather than directly from the front.