Proust himself helps provide the answer and there is a moment when after doubting that he can produce any literature worthy of being read that he has a moment when he finally understands that what he needs is not to strive for some sort of difficult subject but draw on his own experiences.
“So that the essential, the only true book, though in an ordinary sense of the word it does not have to be ‘invented’ by a great writer – for it exists already in each one of us – has to be translated by him. The function and the task of a writer are those of a translator.”
“And surely this was a most tempting prospect, the task of re-creating one’s true life, of rejuvenating one’s impressions.”
Of course the only problem is that you might just run out of time to do all of that…
“But there was a more serious reason for my distress: I had made the discovery of this destructive ambition of Time at the very moment when I had conceived the ambition to make visible, to intellectualise in a work of art, realities that were outside Time.”
If you follow that advice it seems if you want to be the next Proust the sooner you start writing your memories down the better.