Hi Patricia! The holidays are so much fun in the Disney parks and the parades are one of the biggest highlights.
If your budget allows you might want to consider purchasing tickets to
Mickey's Very Merry Christmas Party. This is the annual holiday special event ticket in the Magic Kingdom where all the holiday festivities come together for an evening of fun. The Christmas parade is the highlight of the evening and with fewer guests in the park (they limit the number of tickets sold for each party) it is fairly easy to find a good spot to view it either on Main Street or in the Frontierland area.
If you are heading there to view the Christmas parade make sure it is the holiday parade. It is often done twice each night and I have found it much easier to find a spot for the second parade. I like to sit in front of Tony's in the Town Hall circle as it is much easier to depart the park once the parade passes by. If that does not matter then head to Frontierland and find a spot there.
The dessert party is not for viewing of the parade so be aware of that. You would only see the tops of the floats. The party was developed for the fireworks shows.
The more crowded the park is will dictate how early you will need to find your spot. The main stretch of Main Street will always fill up first.