First of all I gathered together my tools and materials. It is like cooking, makes things run smoother!
I drilled a hole large enough to take the cable, in the floors and at the back of each room. This house was for children so I was using 6v lighting and sturdy cable. (I buy my 6v pea bulbs and bell wire from Squires Model and Craft Tools in the UK. They can often be found in model and craft shops too.) When doing 12v the wires are very fine and smaller holes are needed.
Using a sharp craft knife and a steel ruler I cut a channel in the floor to carry the cable.
I hasten to add that I would NEVER do this to a really old house. The most I will do in an old house is take the wire across the ceiling and through the smallest hole possible through the back wall.
I connected the wire to the bulb holder. With 12v lighting I wouldn't need to do this as I buy 12v tiny pea bulbs with holders and long tails (from miniatures specialists Blackwells of Hawkwell - they can also often be found in model and craft shops too.) It is worth mentioning that many old houses used these bulb holders that I am using, in fact I replaced 2 broken lights in my 1912 house with these and the difference is so slight you can't notice.
I pushed the wire up through the ceiling and out through the hole at the back, laying it neatly in the channel.
I pulled all the wires through to the rear of the house, having made sure I had cut long enough lengths to begin with.
I used a plug-in connector block. These are especially useful if the house is likely to be moved fairly frequently.
Self adhesive cable clips are one of my best discoveries, they can even be used for 12v wires.
Making sure the cables are neat and close to the back of the house prevents them from being tugged out and makes them less attractive to cats!
I made pilot holes for the screws using a small bradawl with a screw end. It makes it easier to get the screws started.
Now the lights are in situ. In the top room I just took the cable across the ceiling. Once the shade is on it won't be noticeable.
The final job was to tape over the wires in the floors ready for decorating.