(that is, when riding in the door zone is unavoidable)
1. Never ride fast (fast=fast enough to result in serious injuries);
2. When a car door unexpectedly opens before me, stay in my path (even if hitting the door), avoid swerving into the next lane unless there is clearly no risk of being hit by an oncoming vehicle. (Because of the low speed, this means avoiding a more serious or even fatal accident at the cost of relatively minor injuries and bike damage.)
Anyway, this may have saved me today from something more serious, when I was riding on the Fifth Avenue (Manhattan) between 37th and 38th streets around 7:45 pm (still rush hour), and a taxi passenger suddenly opened the rear left door in front of the entrance of a building (hotel? 400 5th ave.). I didn't swerve away because it's a congested street with trucks and cars passing on my left very closely. No injury. I just needed to readjust my messed-up derailleur shift and the headlight. Glad I rode slow.
(Btw I finally saw a Citi bike station near 34th street and Broadway today. One Citi bike's saddle was completely turned in reverse.)