Here is a fantastic do it yourself headliner repair, detailed, with pictures. The author is MVS member Red Arrow, and his car is an 850, but the concepts you can apply to any car.
When spraying the 3M adhesive do it in a well ventilated area and wear a proper mark with vapour filters. Its a good idea to cover the ground with paper to protect it from over spray. Also wear some old horrible clothes and shoes because once it gets glue on them its never coming off. Gloves are highly recommended as well. Make sure you have good lighting so you can see what has and has not been sprayed with glue.