We were there for a "sold out" Friday night (12/5). You just have to plan your evening. It is still Magical.
Since everyone is moved to TomorrowLand awaiting the start of the
MVMCP, that is really a good place to steer clear of.
We got to the Park around 4:30 PM, got our wristbands and actually found the rides to be pretty open as people were wrapping up their day at the park. We walked on every ride in FantasyLand + did Space Mountain prior to 6 o'clock. It was a great time to be in the park before the party started.
Another tip on getting your picture taken: at 6:30 there was an extremely long line in TomorrowLand queued up to wait for their picture. We decided to wander over to Fantasyland and at 6:45 found that there were 3 picture taking stations at It's a Small World that were already taking pictures with no wait. Got that done early.
Also good to head to Liberty and Adventureland to ride rides right at 7 with no lines.
It is much better to watch the second parade if you can as the crowds are better then. We watched right on Main Street in front of the bakery. We were in the second row (first row was sitting on the curb) and got there about 15 minutes prior to parade.
Stay and watch the 12 midnight show at Castle if you can. It was great!!