If it is at all possible, try to situate your track layout so that the straight tracks do not run parallel to the edge of the plywood. Doing so makes the trains appear to be running longer distances. This is one of those artistic things, because when the long straight tracks are laid parallel to the edge of their supporting table, your eye is naturally drawn to the relationship between the long edge of the table and the long edge of the track, bringing your view of the train track (and the trains running on it) into relationship with the edge of the table, which is part of the room in which the table sits. By slightly canting the track away from that long table edge, your eye simply sees the train running on the track and you are drawn into the model scene. In some cases this is not possible, such as with modular railroads which need that long table edge for reference to insure that all the modules will fit together, but there are other artistic tricks that can be used in that situation.
The Track Plan in its Environment
If it is possible, it is a good idea to make the track layout slightly smaller than the available space. At minimum, this will give you some room to move the track around a bit as you find the placement for the best visual effect. On a practical basis, especially if the layout is mounted above the floor, it gives the locomotives and cars a small buffer zone should the unexpected happen. (Let's see...What was that formula for the velocity of falling objects?) In any case, moving the tracks back from the edge of the layout will improve the appearance of the railroad scene. However, if you are working in cramped quarters, such as in a briefcase or on a coffee table, this is not realistic.