The steps required are going to very from car to car. I will share the steps I took, as I recall them, to replace my headlinger in my 1989 Caprice 9C1.

Tools Needed:
TORX bits
Phillips screwdriver
Standard screwdriver
Needle nose pliers
Headliner material
Spray adhesive
Wire brush
X-Acto knife

Optional stuff
Dynamat

Advice section
My first piece of advice for doing this job would be to remove the front seat(s) from your car. It's not really required. But it will make the job alot easier to do. My second piece of advice: Get someone to help you take the headliner out and put it back in. Once again, it's not really required. But it will make the job go much easier. Third: Buy your headliner material and adhesive from Eastwood, see the link at the bottom. They seem to have the best kit that I've found. At least it comes shipped to your door in a hard box and all of the contents shuold be undamaged, unlike other companies I have used. Fourth: While you have the headliner out, remove the old hard sound deadening material from the roof and cover every square inch that you possibly can with Dynamat. I did and I can't say enough for how much quieter it made the interior of the car.

Let's get started..
Begin by removing the sun visors using a phillips screwdriver. Next remove the coat hooks using a phillips screwdriver. Then remove the dome light cover using a flat blade screwdriver to pry it out carefully. Now use the needle nose pliers to unscrew the small bolts holding the domelight in place.

Now move to the rear of the car. I began by removing the corner pieces around the rear window first, then taking all of the trim off across the top of the back window. You will have to break the tab pieces that hold this top piece in place. Next pull down on the c-pillar trim pieces to move the top part of them out of the way. Now carefully removed the cloth c-pillar pieces. After that I removed the b-pillar trim. To do this required a large TORX bit. This was needed to get the upper seatbelt mounts loosened. There are also several small screws that hold each pillar down in place. After the b-pillar trim pieces were out I removed the metal trim pieces that run along the top outside edge of the headliner. To remove these, stand in the open door and look at where the trim pieces meet the body. Starting at the back of the back door, pry down with the flat blade screwdriver, moving slowing from the back to the front until the part comes loose. They are held in place with a couple of tension clips and will need to slide back about and inch to get them off of the a-pillar trim. Once you have these pieces out, remove the retainers for the headliner using a phillips screwdriver. Now you can move to the front of the car.

Now move to the front of the car and remove the a-pillar trim using a phillps screwdriver to remove the screws. Next remove the metal trim piece that runs along the top of the windshield. Again you're going to probably have to break these trim pieces to get them loose of the trim and the body of the car.

OK, let's see, you've got the trim around the back off. You've got the trim along the sides out. And the front is out too, right? That headliner should just about fall out to the floor now. Now you've got to get it out. It will take some bending and some twisting. But it will turn and come out the passenger side front door. Now that you've got the board out, you are probably worried about having broken some of the pieces of the board off. In particular those points at the front where the visors were mounted. Don't worry about it. We'll fix those soon. Now take the board and lay it down on a flat surface. Pull off all of the material next. This will leave a bunch of foam stuck to the board. Take your wire brush and gently rub it back and forth across the board to work all of the leftover foam loose. Do this to any pieces that may have broken loose also. Now those broken pieces and cracks in the board....You've got a roll of duct tape right? Get it and get going. Use the tape to strengthen any of the cracks and to patch any broken pieces back into place.

Now take the new headliner material and roll it out on top of the headliner board. Center the piece of material as best you can. Try and position it so that you have as much extra material as possible. Pull back the material from the front and let it lay on the other half. Take the spray adhesive and spray it onto the exposed headliner board and onto the foam side the material that you pulled back. Once you have it all sprayed on, let it sit for a minute or two. Next pull the material back into place over the headliner board. Take your hand and smooth the material down. Be careful not to press too hard. Repeat these steps for the back half of the headliner board. Now take that x-acto knife and trim the excess material. Try and leave about .75 inches of material all the way around. Trim out the holes for the visors and the domelight too.

Now that you got the new material in place, get your friend to help you get the headliner back into the car. Once you get it in place, re-install the trim in opposite order that you took it out.