Step 1: Star power
You're going to need a lot of it. The Wire specifies a minimum of three famous people per photo. Kim Kardashian's snap from the Vogue Paris party works overtime because it combines luminaries from both the celebrity and fashion worlds.
Step 2: Consider arranging an event for everyone to attend
If there's no big occasion when all of your besties will be gathered together (in full hair and makeup) in the near future, create one. Did Gwyneth look at the calendar and say "Oh darn; the Emmys aren't until August. When will I get Nicole, Chelsea, and Naomi together before then?" Heck no! She threw a #girlsdinner and invited the whole crew. She didn't even worry about the less-than-optimal lighting for her fun group selfie.