As with most things Disney, being there early is key:
> Line Up Before the Party Starts:
– A huge part of MNSSHP is character meet and greets. Both fur and face characters are in every conceivable corner of the park, but you don't need to bother them unless they're specific to the party.
Every year there are a few must meet characters. This year the big ticket are Jack and Sally from classic Nightmare Before Christmas. These characters (however ugly the design is…) are extremely rare at Walt Disney World, and the line will reflect this throughout the night. If you have any hope of enjoying the party without waiting in a long line during the limited hours available you need to line up early. Join (or start) the queue no later than 45 minutes before 7:00 if you have any interest in meeting these rare characters. The same rule applies for the seven dwarves and the princesses/princes.
It is possible to meet all characters available…but you will have to dedicate your entire evening toward the process.