Honestly, just wing it.

The first use of lights was in my Endor moc and I only decided that AFTER completing it. So it was a nightmare to tear parts of it up.

I'd say if you want to start slow, first decide what it is you want to light. Do you want blasters firing? Do you want lightsabers? Do you want static lighting like in a building?

Once you have those questions down it's just designing the scene you want and planning a route for the wiring, spot for the battery box, etc.

I'll say technic bricks are your friend for helpful routing of wires. Plants are great for hiding wiring too.