My thoughts on the subject
Fist lets list the mane 6
Twilight
Rarity
Fluttershy
Rainbow Dash
Applejack
Pinkie Pie
I'm going to count Twilight out since we already know how she interacts with all the others.
Rarity + Fluttershy: They have gone to the spa together for a long time from what I can tell. They also both like sewing, even if Rarity didn't know it at first. I like the squee comic where Rarity helps Fluttershy after she drops her ice cream and then there is cute.
Rarity + RD: They probably didn't hang much. They are different, but knew each other enough to knew they had different interests.
Rarity + Applejack: Same as with RD. Maybe a little more hostile since Applejack likes to get down and dirty.
Rarity + Pinkie Pie: were probably acquaintances since they all were. Nothing really going on.
Fluttershy + RD: They've know each other forever. They were probably friends, but didn't do much together.
Fluttershy + Applejack: Were probably acquaintances through RD or just from meeting. Applejack would also help supply food for the critters and Fluttershy would help with advice.
Fluttershy + Pinkie Pie: They might know each other a little better for whatever reason. They seem at ease around each other and I liked the scene where Fluttershy got annoyed at Pinkie and said that she was a year older than her. ((RAMBLE MODE: ACTIVE!!!))
RD + Applejack: Shipping, shipping everywhere. They like to compete and are probably good friends IMO. I like to think they are best friends if we are not talking about love relationships.
RD + Pinkie Pie: Pinkie Pie is a stalker but they are friends for whatever reason; as seen in Griffon the Brush Off. More ship fuel.
Applejack + Pinkie Pie: They might collaborate with food, and they are both earth ponies. Probably know each other through RD.
Overall, Rainbow Dash seems the most connected beforehand of any of them.
Then Twilight came and made them all friends.
AND THAT'S HOW EQUESTRIA WAS MADE!
Anyway…
TL;DR
I aught to go to bed. And then I have to do homework all day tomorrow. loljk, i poni and homework at the same time. So I'll actually be on all day! Adios!
Okay, last edit before bed
I really like her mane!