#1- EAT LESS. This is the top tip. Eat less at breakfast, lunch and dinner. Remember, we don't need 4-5 meals a day, we need 4-5 feedings a day.
#2 Plan to Fail- as above, don't eat normally if you know you are going to attend a party. Eat sparingly during the day leading up to a party.
#3- Plan to Fail Part 2- get extra workouts in. Expend more calories in anticipation of taking in more calories.
#4- Forget all the stuff about sparkling water and celery. Just decrease your intake on "party" days and up your activity.
#5- Eat protein. Protein is filling and satiating. Better to eat chicken wings than chips in the mad, mad world of holiday parties.
BOTTOM LINE JUST EAT LESS!