In my experience most novelists have more ideas than time. The problem isn’t finding good ideas or premises, it’s having the will to finish the novel, grit in the term that is now becoming popular. I think each story idea must satisfy four criteria to be useful for your novel.
You must be passionate about it with enough passion to sustain a year’s work
You must be able to make others care about it
You must be able to dramatize it (with little explanation)
One thing you don’t need is an idea that you are given but care little about. Many writers hate parties, or at least hate admitting their passion or profession, because too often they’re approached with, “I have this great idea for your next novel.” I know of no novelist who would be interested. I suppose there are some, but I can’t see how someone can write another’s story. The suggested idea could turn into an interesting story, but then everyone is presented with dozens of ideas every day.
So, if you don’t have a cover story for people you meet at the party, perhaps you can use this dialog. “Oh. You’re a novelist. I have this great idea. You should write about my Uncle Mel in WWII. He was awarded a Bronze star for saving his platoon.”
“That sounds like a wonderful idea. Mel’s the protagonist. Who’s the antagonist?”
“Um, er, uh.”
“Yeah, you have to have at least one antagonist for a story. Also, what is the inciting incident?”
“Also, if you’re familiar with the action, you should be in a good place to describe the setting. Sounds like a perfect place to start your writing.”
And if he really can answer those questions and a few more like them, and persists that you have to write the story, tell him, “I guess I could write about that. It takes me a year to write a novel, so I’ll need $150,0001 (or whatever 6+ digit number you can say without out giggling) for the job.
1If you multiply your salary by 2 to 3, you will come up with about the number that you cost your employer. Or, for the full time writer, your last salary adjusted for inflation. Then add enough for the inconvenience to dealing with the requestor, their subject, the research, and for being tied up on their project all year. That should give you an idea of a reasonable fee.