If I've done a bit of riding with the person I'll get within 6-10 inches of their wheel always trying to stay a bit off center left, in case we brush I know which way to go. If it is someone I don't know well, will stay 12 inches or more behind until I get a feel for their riding style and then will creep up a bit. With folks I know, I know they will be sharp and will will point out any holes or debris, also will inform me of anything up a head that will cause a change in pace. On a steep hill will back off and let everyone work at their own pace, form back up ath the top.