Personally, I'm still in the planning/layout phases, but here's what I've read on the subject:
It helps to have a scale drawing with gridline reference. For a 4x8 layout, I'd suggest 6" gridlines. Reference your drawing when laying track and make sure everything fits. It also helps if you have cork roadbed so you know exactly how everything fits. Once everything is in place, use a light dusting of spraypaint over the finished layout. This covers the glossy finish on the railroad ties and makes them more realistic, and the paint on the tracks is easily cleaned off with an eraser type track abrasive.
When pulling up the track, be sure to label the track, corkboard, and plywood so you'll know what goes where.