It's pretty easy, actually. Cleanse the area first. (there are already very good explanations on how to do that already on this site... just use the search)
Then you have a rather wide variety of options to choose from. You can make a peace air spray that you put in a spray bottle and spritz in the air. Heck, if you get a lavender, jasmine, or yang-lang scented air freshener, or scented candle, you can bless that to bring peace.
Or maybe a bowl of blessed potpourri placed in strategic points. Or even, you can make a blessing powder and sprinkle it in the four corners of the room.
The thing with these is that they have to be redone on a regular basis, from every one to ever three months depending on how bad the problem is. Also, if the peace is visibly broken at one point or another, it's a good idea to redo the spell over that area.
Also, some of these *stick* better than others. The powder, for example, may need to be done more often, like once a day for a week, then once a week after that. You only need to use a pinch per corner, then visualize a circle of peaceful energy over that space. It's ok if it gets vacuumed away! (It just releases the energy into the environment when it's sprinkled.)
If you want ideas on blends to use, just let me know which approach would be most appropriate to your situation, and we can go from there.
You could also use some blessed blue lace agate hidden around the areas you want to protect. You can get chips of the stuff and put them behind picture frames and the like... I don't know how much control you have over your surroundings.