I really didn't think it would be possible to throw so much parties! So here is my strategy:
My sims started out already married, so they could do the flirty interactions sometimes requested during the holidays easily.
They had the following traits:
-Sim #1 (responsible for organizing parties and leader of the group): outgoing, party animal, insider, party animal aspiration
-Sim #2 (bar manager): creative, party animal, outgoing, mixologist aspiration
I put as lot traits: homey, convivial, party place.
My sims created a club with cheerful / outgoing / dancing machine sims and got the “rally the troops” and “good reputation” rewards, the friendship, funny and flirting bonuses and the playful /happy/inspired and romantic buffs rewards that I used according to my needs for the different parties.
The guests were always the members of the group (along with a few other sims).
My sim #1 completed the “party animal” aspiration as quickly as possible to get the reward trait that allows you to start all parties at bronze level.
From there, I was able to organize around twenty parties per day (up to 25 on several days) because we only have to achieve the main objective to get the gold level. For example, “calling guests to the table” for a dinner party, or chatting 10 times for a private party, etc.
While my sim #1 was in charge of organizing the parties, my sim #2 was participating and also making money with the mixology skill.
He prepared the most expensive drinks possible again and again, in order to sell them.
After having tried several kinds of parties (but always, every 5 parties, the "incognito costume party" because the rewards are really big, from D6 (when my sim 1 finished his aspiration) I only kept the following 5 parties because they were the ones whose main objectives were the quickest to achieve:
-slumber party: sometimes (about once in 3), the main objective “go to bed” is achievable from the start of the party, so the gold level is achieved in a single interaction. Other times it takes a little longer but can still be done quickly.
-private party: 10 interactions with guests to earn gold
-dinner: just call guests to dinner to get gold in a single interaction, that is really the quickest party to win
-baby shower: 6 baby talks with guests
-incognito costume party: 12 discussions about costumes
On D1 I had 4 gold parties and one silver; on D2 5 gold; on D3 6 gold and one silver; on D4 10 gold (from the end of D4 I already had a bonus for the parties without having completed the aspiration, I think it was due to a club advantage but I'm not sure); at D5 13 gold; and from D6, aspiration completed and between 20 and 25 gold level parties each day.
Thta was a fun challenge but really long to achieve! I learned a lot about parties