A basic train set usually comes with an oval of track. The dimensions of your oval should be in the instructions. Find a table or floor space large enough for your oval.
Do not place your track on shag carpet, the track won't lay flat and your locomotive's trucks may become snarled with carpet fibers.
Lay your track pieces out in the space you've selected without connecting them. This way you'll be certain that you have measured correctly and have enough room for your oval. You don't want to discover that you didn't use a big enough space when you have half of your oval track pieces connected.
If your train set includes piers to raise the track for a crossover, pay close attention to the placement of the piers as shown in your train set's instructions. Placing piers too close together can result in to steep a
grade for your train to climb.