here's an infinite number of ways to do it, but I generally do it the same way as previously mentioned. I try to work on no more than 3 or 4 boards at a time although I have worked on 10 or 12 at a time. If you get too many boards out there, the task can seem overwhelming and you can easily become discouraged.
I usually work in this order:
1. track (fixing spline point elevations as I go)
2. terrain (bringing terrain to track)
3. adjust remaining terrain to my liking
4. add buildings and roads. sometimes bldgs first and sometimes roads first
5. a base texture, usually copied and pasted
6. signals
7. foilage
8. details
I find it important not to work in your signalling and test the route out as you work. If you get the route too big before testing, then it can become a daunting task to find problems with your layout.