IMO, the number one factor is desire.
I'll be completely honest. I'm always interested in remembering my dreams, and I like to complain a lot about recall in my DJ, but.. interest is not enough.
Of course everyone here is fascinated with dreams, but it's hard to maintain enthusiasm every single night. Many nights I go to sleep, hoping, but not strongly wanting, to get lucid or have good recall. Sometimes it even seems like I don't want it, because I'm lazy, and I don't want to record ten dreams in detail.
This never lasts, and if it goes on long enough, I begin to very strongly desire to have lucidity and recall. Or, I may see or hear something that similarly inspires me. Now, if I go to sleep in such a state, bordering on obsession, I almost never fail to have ridiculously good recall, and relentless lucidity, in proportion to my desire.
The problem is, it's not enough to think you really want it, or tell yourself, etc. . It has to be genuine desire. If it is, I believe it's possible to have and remember incredible dreams under any circumstances.
Having said that, I do agree strongly with all the other factors, and of course good recall is possible without desire; it's sufficient, but not necessary. It is, however, the only seemingly constant factor in my personal experience.