Writers have to imagine entire worlds, people and situations inside their heads. Then they have to take those thoughts and put them on the page. It's a personal process, and because of that you have to know how to isolate yourself.
Can you write in a noisy room filled with people? I can...because I can isolate. Clearly it's not an ideal writing situation, but I'm guessing that you don't live in a large mansion with lots and lots of rooms. I'm guessing you live in a normal-sized home, and that other people are sometimes around you.
And when that's the case, you're going to need to know how to isolate yourself...even when you can't lock yourself in the attic and write, a la Josephine March (Little Women reference).
- Pick a spot, any spot: Choose a location in your home that's your "spot." I sit on one end of my couch with my laptop. I'm used to writing here when it's quiet, and that makes it easier to write when the room is crowded. You're already in the mindset that you're going to write from this spot if you make a habit of working in the same place.
- Tell the others: Make sure that everyone in your household knows that this is your writing spot. When you have the keyboard under your fingers and that weird look on your face, it means that you're writing -- and that means they have to leave you alone unless it's an emergency. Family members of writers may have to hear this many, many times before they start to get it.
- Focus: Tune out. When you're writing, focus just on the screen. Get used to writing with background noise by turning on the TV or listening to music while you're working. Start out at a low volume and gradually increase the sound to get yourself used to it. Focus is like a muscle; you have to work it out and get it strong before you can tune out the entire world to write.
Don't Be Extreme
There are going to be many times when you have to isolate yourself in order to write. You will have to tune out the world, focus on your words and ignore everybody else's. But don't go to extremes. Writing by its very nature is lonely. Isolate too much and you might drive yourself a little crazy.
Remember to spend time with other people and spend time getting out of the house. You need to interact with others, but when it's time to write it's time to stop socializing.