I would negotiate for a certain number of paid trips back to HQ every year, such as at least once a quarter -- you need to keep your face in front of people to avoid being forgotten/overlooked/first in line for the next layoff.
Ditto the separate office concept. I find it very distracting when DH and I are both working at home at the same time. If this were more of a regular thing, I would need to set up a separate workspace for me.
If you have kids, make sure the office has a door on it. :-) I know it sounds basic, but my current office doesn't (took it off in a reno and never replaced, because the hall is small with two other doors), and BOY do I miss that!
Know how you work and make "rules" that hold you to it. My problem is procrastination. At the office, I naturally get spurred out of it, because people walk by and I look up and see the time and think, "oh shit." At home by myself, man, sometimes I look up and it's noon -- and by that time, it's "oh fuck." So when I was full-time WAH, I had to make rules for what time I started work and how long I allowed myself to break for (so I didn't throw in a load of laundry and get distracted by the dirty dishes in the sink and then remember I needed to defrost something for dinner . . .). Your situation will be different, of course; the key is to be conscious of your own pitfalls so you can plan workarounds.