Especially when writing, it's good to have a space to work without interruption or distraction. But if you have to work in a busy office, here's a simple trick to create that space.
Get some large, over-ear headphones and put them on when you need to focus. This has the dual effect of shutting out background noise and creating a visual cue to others. People are much less likely to come and talk to you if they can see you are shut away (this is why over-ear headphones are better than the in-ear type; they are more visible).