Generally, the buffer+ should be the first and last thing in your effects chain.

Guitar --> Buffer+ guitar in --> buffer+ loop out --> effects pedals --> buffer+ loop in --> buffer+ amp out --> amp.

Some vintage and reissue fuzz pedals might work better in front of the buffer+, as they're actually designed to load down the signal a bit, which is what the buffer+ protects against, but usually the buffer+ will be first.