http://www.horsechannel.com/horse-news/2014/11/how-to-longe-your-horse.aspx There's a picture with the lunge line through the bit, over the poll, and clipped onto the other side of the bit to this site.
I like to run the lunge through the bit ring on one side and attach it to the ring on the other side, over the horse's poll. It puts less pressure on one side of the horses mouth and kinda evens out the pressure, but they also make attachments that connects to the bit then there's a ring underneath the horse's chin for the lunge to attach to, rather than to the bit directly.
Ok, I had another question. My trainer likes to lunge with a bit attached to the line, I really don't like that. What's your opinions?
If you plant your elbow at your hip and lower your centre of gravity it should help solidify you and prevent you from being literally pulled around. Making sure to keep on them with the lunge whip is important too, if they have to think about moving forward, they will be less likely to haul you around, as Brenna said.
But what if they are literally pulling you around?
Because they're stronger than us, When they pull, you have to get after them and push them forward through it, rather than just pull back. This way, they have to convert their energy to foreword momentum rather than sideways. They will eventually learn that the only way out is through the front, and you will block that with halfhalts.