If your glasses always slip down nose, this means the size of your glasses is not suitable for your face. You can go to store where you buy your glasses to ask them to help you adjust the distance of the two temples. In your case, you should ask them to tight the screws which connect the frame and temple. If slipping still happen, you can add a pad on your ear touched part of temple.
Normally glasses from slipping down nose because the glasses' nose pads are not OK. They should be adjusted, so you go to the professional optical shop and ask them to help you to free adjustment. In addition, there is another reason---the glasses legs which need to be bend into a point, they can roast the legs with special fire, and soft bend according to your demand. The effective way is to stick around the corner of glasses' legs with preservation film as tight as you can. It is not easy to slip down.
You may have chosen the wrong type of frame for your face,You should get the frames with the rubber or plastic nose supports. This way when your glasses get a bit loose, you can take a pair of pliars and gently squeeze the two pieces closer together for a tight fit on your bridge.Â
If you can not afford new frames, you should get some duct tape, stick it to the inside of the bridge support and remove it. Keep doing this until there is enough adhesive left behind from the tape that it actually sticks to your face when you put on your glasses.