It's very complicated and dangerous...I suggest you bring your Leaf to my house when you get it and I'll drive it daily so you don't have a thing to worry about!
I suspect Nissan will distribute recommendations, it may, well, be possible to put the car into a 'storage' mode like the Tesla Roadster has that will charge/discharge the battery to about 50% and then minimally cycle it at intervals. If it is not possible to keep it on a charger during your storage time I'm not sure what the recommendation would be and would assume you'd need to inquire with Nissan...but going back to my first paragraph, it is probably best to have someone you trust drive and charge it intermittently rather than just store it.
You didn't say what "long term" is for you? I think a few months will be no issue, but if you're talking about 6 months, or a year or more, that may be a whole different and more complex issue.
