The first think we have to keep in mind is the available space; then we must begin to plan a suitable track plan accordin the chose scale. If we like to see long trains running freely in the layout we must foresee long stright sections, otherwise, if we prefer loading operation in big stations, we can plan a point to point layout.
It's important to have a clear idea from the beginning, so we can avoid to modify our work during the construction.
There are differents solutions to build a layout:

 

1. Stright:
   of rectangular shape, it is disposed on a side of the room; suitable for point to point layout or diorames;
2. L Shape: the structure, composed by two rectangular sections, has a 'L' shape; it can be used to have interesting layout keeping free space in the other side of the room;
3. Along the room structure:
   the layout runs along all the walls of the rooms; this is the most beautiful solution as we are surrounded by scenery and rolling stocks.

 

In all cases we must be able to reach each portion of the layout, to build, maintain, but also to bring derailled rolling stocks. If the structure runs along the wall, it must be no depth as 1 meter; otherwise if it is detached from the wall we must foreseen about 70 cms from the layout to the wall to walk around.
Now we can develop the idea of our layout: don't forget to draw, draw, try and try before the final track layout. There are lots of books and web sites showing lots of ideas: the more we look before the more we'll have pleasure after.