I tend to look through the meme for prompts I like and think I could fill and I bookmark them. Then, later, I go through my bookmarks and fill the one that appeals most right then.

As for what and why one prompt appeals over another? Well it tends to need to be a gene I write with characters I like and it helps if I can easily imagine a scene. I, personally, also tend to pick prompts to bookmark that can be filled properly in a few thousand words and don't have a lot of meta discussion (though that's not always the case). But that's just my thing... I like to be able to fill a fill in one go (I tend to write a fill in one go at night. I have a lot of fills).

I doubt this is helpful bit yeah. My process.