At first it can be a lot more scary approaching a group but it can also be a lot more beneficial.
I will still go direct but I will say something along the lines- "Hi, i know this is random and i dont want to embarrass anyone but (pause) i was walking past and i have to say that your'e friend here looks absoloutly stunning today" (in front of everyone). I will include "and i dont want to embarrass anyone" because it shows social intelligence as you understand you are doing this in front of all her friends.
Most of the time the friends are just as friendly or even friendlier than the target as it is entertaining and even exciting for them to watch this.
Include the friend in the convo as much as the girl your'e after as not to exclude her. This can be so beneficial as switching between your'e target and her friend results in a lot more conversational threads/topics to go down which is great if you sometimes run out of things to say when you are talking to one girl on her own.
It really does help approaching groups as sometimes the girl you go direct on goes shy but her friend is really chatty so you can talk to her friend a bit more until your'e target gets more comftorable with the situation. I have even had the girls friends say stuff like "you can take her away for two minutes if you want" which is awesome as having her friends acceptance of you and you're approach is really important.
Hope this helps.
p.s. After you have approached groups of girls the next step is mother and daughters
Now thats a rush.