How do you run a successful party to finish Reaper's rewards?

• Throw a party and make sure that you've checked the box for Goals And Rewards. House parties are probably the easiest for this requirement. 
• Complete the Main Goal. That's enough to get Bronze and it's usually needed to get anything higher than Bronze. 
• Complete as many of the minor goals as you can. That will get you to Silver or Gold, depending on how many you can finish. 
• Do the easiest goals first. It's hard for me to get Sims to do things at the same time, so I usually avoid goals like Have 3 Sims Listen To Music or Watch TV. Instead I choose things like Tell Jokes, Tell Stories, Thank For Coming, etc. 

Make sure that you have a high friendship score with whomever you invite to your dinner party. My first time attempting it, my sim didn't have a very high score with the 2 she invited and I didn't get a good score. So I tried it again. And it didn't change anything. I saved my game and went back later, and this time I made sure that I had a higher friendship score with the ones I had invited and by the time the event was over, I had completed it to the satisfaction of whatever is scoring this thing. But for me, saving the game and leaving that lot, then going back into the lot AND making sure that score was high. Then I just had to wait for a Wednesday night for the ghosts to visit a pub and I was done.

There was no ghost party to go to. You only have to go to the pub WHEN the ghosts are there on Wednesday night to complete this one. 

Good luck!