A leaflet inside the blackdog box tells u how to do it, but it basically says of the top of my head:
The closer the pickup is to the strings, the more output it will have.
The further away the pickup is from the strings, the clearerthe sound will be, but slightly less output!
so just put it close to the strings, play a little lick/riff, then gradually move the pickup away from the strings until u have a balance of output and clarity (so it will have decent output, and clear tone).
Thats what i do, but i always think its best in the middle cos u can always turn sound up (unless u have your amp on 10!!)...but you cant make something sound clearer...well not easily...