Getting into the zone takes time. Every interruption takes its toll; research has shown that on average people take 23 minutes to regain the level of focus they had prior to an interruption.
You can minimize the amount of time spent regaining focus by implementing a rule where you spend half your day alone. Naturally, you can host meetings or chat with co-workers and collaborators during the other half. Collaboration software company 37Signals (authors of the bestselling nonfiction book, Rework) write:
Set up a rule at work: Make half the day alone time. From 10am-2pm, no one can talk to one another (except during lunch). Or make the first or the last half of the day the alone time period. Just make sure this period is contiguous in order to avoid productivity-killing interruptions.
This type of practice isn’t necessarily restricted to the workplace; rather, this is even easier to implement (and perhaps more effective) for freelancers. By spending less time regaining focus, and you’ll have more time to build awesome things.