This section will hopefully give you an insight into the methods used in designing and constructing a model railway, or at least one way. There are no right and wrong ways but there are a few 'golden rules' that if followed usually result in a finished model that gives satisfaction. You never stop learning and probably always feel like next time, you can do even better!
PLANNING - THE KEY
Plan, draw, sketch, plot and stick to your plan ...
Golden Rule 1 - Planning.
The key to a good and nicely working model is planning, not only the track plan but the whole concept. Design your plan, think about the operating potential, layout of buildings and if your plan is purely fictional, try to work it so there would be a reason for it to exist should it be for real.
Railways were always built for a purpose so try to invent a purpose for your model be it quarrying, dockside, brewery or loco works etc.
Once roughly planned, draw it up accurately. There are several model railway track planning softwares available, some for free, so you know the design can actually be made and curves blend nicely. These will also give you a list of the track components needed to build it which is very useful and you can tweak the design at this stage.
Once happy with the design and you know it fits into the space you have available, print it out then using coloured pencils, work out the power feeds and polarities, checking for short circuits, any section breaks needed and work out by what method you intend to connect it all up.
As a newcomer to the hobby, you will need to decide whether to go old school analogue DC or modern DCC (Digital Command Control). It can be argued that going DCC from the start is best as DC is the old way and all new locos are DCC ready, if not already equipped. Your budget may dictate this as if you can only afford used locos chances are they will be pre-DCC and so a lot cheaper. A problem may arise later if you decide to change to DCC as they may not be suitable for conversion, especially if you want to add sound. Many DCC equipped locos can be run on DC but they may need setting up on a DCC system first so this may not be a cost saving way to start.
There are many ways to wire up a layout regardless of the chosen method of basic DC and digital DCC loco control and although track wiring can be simplified with DCC, to go fully digital in route selection, lighting and signalling can also get very complicated. More like computer programming than playing trains!
Loco operation under DCC is also more complicated and needs more preparation of each loco you intend to run but adds realism.