When your eyeglasses keep slipping down your nose, you need to remove them and clean your face. Use some oil-reducing face wash with warm water and focus on and around your nose and lather it up. Oil collects on the sides of your nostrils so you need to pay attention to this region as well.
Since you cannot use a face wash every time you wash your face during the day, try washing your face with cold water to close the pores and then dry with a towel. This will keep the glasses from slipping down for a while.
You can use a tissue paper to clean your glasses, especially the area which rests on your nose.
Brush some baby powder on your nose with the help of a makeup brush or your finger. Baby power can absorb moisture and prevent your glasses from slippign down.
You have to position your glasses so that your eyes are right in the center of the lenses. Any adjustments in the glasses should be made by keeping this position in mind.
Sometimes the temple arms are not properly leveled and contribute towards your problem. You need to lay the glasses on a table and gently bend the arms a little inward before trying them on to see if they fit properly.
Earpieces also play a major role in keeping your glasses in the right place. If the glasses are too loose, you can easily bend the earpieces inwards and if the earpieces are bugging you then this means they are already too tight and you need to bend them outward to take the strain off the back of your ears.
Positioning the nose pads properly is another factor you need to keep in mind when fixing your eyeglasses. If your glasses are too low, then you need to press the nose pads together and vice versa if the eye glasses are too high. Do this gently so that you do not break the nose pads as they are extremely delicate.