I was just chatting with a Tufts alumna, and she had the following tip to pass along:
"A UN job I'm applying to had 3 vacancy announcements (same position descriptions) with different deadlines (all around August). I decided to apply to only one, thinking that it wouldn't look good if I applied to all three of them. I picked the one that was most recently posted instead of the older announcements.
I called the UN HR department just to make sure I was correct and they told me to apply to all 3 of the postings. The person I talked to told me that even if they like me and would consider me for the first available post, for instance, if I do not apply a second time, they cannot officially call me."
For more advice from Tufts alumni working in international affairs, check out our International Affairs Virtual Forum archive: http://careers.tufts.edu/students/additional/webresources.asp