Eh its just all about managing your time well is all. For example making rough outlines on your break and lunch time then do real writing when you're done with everything else. That's basically it really... At least, that's how I usually do it. Although... I'm so swamped with stuff that I get...
At least 20 chapters and / or at least 20K words total. This only applies to *old* works though. If it's a new work, I'd read too see if it's got potential.