My best tip? Go to Downtown Disney during the day and spend the evening at the Boardwalk. Blasphemy, I know, but I'd avoid the parks like the plague on NYE.
If you want to see the fireworks at MK, watch them from the beach at the Poly. If you absolutely MUST go into a park that day (heaven forbid it should be MK!), I will back slowly away and let others give you good advise.