For the haloween MEP, I told them a genre to edit with. For the stronger MEP, I told them a specific message to convey in their editing. Really, so long as all the tracks have a connecting thread, it can make for a good MEP with just one song.
for audio cutting? Well, there's a lot of different opinions on that one. I usually cut them up in easy to edit chunks. For example, one editor gets the entire chorus, while another editor gets a buildup/regular part. like in the stronger MEP, you'll see that there's an opening bit, followed up by another editor taking the upcoming chorus, then another regular bit followed by another chorus. Then we have a buildup bit and the final chorus/ending.