I think you've gotten some great advice thus far. (And it's also interesting to see how others handle this little writing issue :]).
Personally, I do two things. I'll sit down with a notebook and write an outline, never too much, just something to help me order my thoughts because sometimes even when you have a plot the little details can still be jumbled. Anywho, after that if I still can't write the "opener" I fast forward to what I can write. I find that once the creative juices are flowing everything else tends to come easier. Eventually the "opener" will just magically come together because I'm in "the zone" lol so I just end up going back and filling it in.
No worries though. It's definitely not just you who has this problem and with time you'll get it solved. Just try a few strategies and before you know it the story might just be writing itself
