hey there I did have an awesome guide but im pretty sure It got left on my old pc... any way here is a pretty good link:
http://www.automedia.com/Headliner_Repl ... 000717hu/1
step by step with pics not exactly the same set up as a mini but u get the idea there.
Main points to remember is to do a "dry fit" where as once you have inserted the rods (now located in the new lining) into rail go to front/back (back and forth) and use strong bulldog clips (carefull to keep to the edge that will be covered by the rubber seals, but regardless keep to the edge, to avoid stretching the fabric into the void, also you dont need to make it super tight at this point clips wont hold anyway, just get it even) as I was saying go back and forth from front to back at this point setting the lining evenly then when you are happy do the left/right direction same theory.
One you are happy with the dry fit go in same manner (front/back then left/right) and using rubber cement or contact cement with a small brush, remove the clips one by one and *evenly* tighten the lining, glue then re-clip for security (if the clip is going to stretch or damage the fabric, leave it - just make sure the glue was tacky enough to hold tight, or leave area till last if possible when lining is mostly well attached)
Just use your judgement, and keep checking it as you go it will be fine.
Let it settle in for a bit and if you have a couple creases, just use water in a spray bottle and a hair dryer or steam (moisture and heat however u wish) on the area. Have fun hope this helped!