If like me you don't understand electrics you'll need someone to either wire it, or at least help point you in the right direction.
For me Roger Elkin of The ET-MRC helped me out. I sent him a diagram of my layout, where I wanted locos to be held and he then sent it back as a wiring diagram - so many thanks Roger!
Now it's Sunday 6pm and I spent the best part of two hours trying to solder a section of the layout, only to find out I was soldering the wrong end of the layout. It turned out the problem was a broken connection via the switching box, once I'd located the problem, I fixed it in 30 seconds.
So here's the second tip, before re-soldering something, check to make sure it's the correct connection!