Need I say more?
Since this is in the bathroom, we are using greenboard. Greenboard is for applications in wet areas. Its a heavier than regular wallboard. It's not as flexible either. It IS just as messy though. Thankfully, we don't have to do all the walls since we still have the existing outer walls. There is some patching to do though from removing the tile and moving some plugs from the electrical/plumbing work.
Hanging drywall is pretty easy. You want to cut out with a drywall knife for all electrical outlets, heat vents and plumbing. I learned a super cool trick years ago for marking the areas. Let's say you are marking for an electrical outlet. Take an old lipstick and run on the edge of the outlet box. Lift up the drywall where you want to install it and gently press against the box. Pull the drywall away and on the back is the area that needs to be cut out marked in lipstick! This can then be done easily with a drywall knife and you don't have to worry about sawing in a live electrical outlet.
You also want to run your screws down the stud to hold the drywall when installing. Drywall comes in a standard 4' x 8' sheet. It's easiest to run the drywall with the 4' going parallel to the floor. That way you can see where the studs are. Screws should be set about 2' apart.
Once the drywall is in place comes the fun part, mudding and taping. This will help to hide the seam and if the drywall shrinks or swells it should help with cracking. You want to put atleast 2 coats of mud on, sanding in between coats. Make sure you cover anything that you don't want covered in dust. It goes everywhere and is a royal pain to get off. You also want to dry the mud fully inbetween coats and before sanding.
The new drywall/greenboard needs to be primed before painting. That is where I step in. Painting is my department.
Now, to go and pick out colors....