I think the best thing to do is talk it over and plan out in the OOC. If you don't, you run the risk of people all going after the same target, plus your writing can be improved by stating what's happening and acknowledging who is going where.

[i]Eg: Char A ran off to fight the east, knowing that Char B would be taking on the west[/i]
^^^
That's not autoing, or powerplaying or anything since it was discussed prior, but it's a way to collab without having to write together.

Something to keep in mind as well is the time and strength needed to defeat the opponents. Is it a mob that is being slaughtered? Are there leader characters in amoungst the enemies? What will happen if you break their ranks, will they flee or fight back?

Thinking off topic about it, but tabletop games like Warhammer and 40k are probably the best way to relate as you can have a few hero characters vs a group of orks or tynarids and each race reacts differently to different situations.