A lot would depend on the particular world. Is it near the border, or in the interior? Isolated, or on a J-1 or J-2 main? And so forth.
High population, high value worlds, especially those near the border, will have as many SDBs as they can afford. A few of these will be in orbit around the mainworld at any given time; most of those will be docked or parked near orbital elements of the starport, at various states of readiness. The rest will be stationed at strategic points around the system -- likely 100d ingress points around the mainworld, gas giants, important secondary worlds, and so forth.
Imperial Navy ships will tend to move around. If they stay in one place too long, potential enemies and evildoers will know what to expect. So fleets and fleet elements get moved around semi-randomly. The major systems near the border will always have significant fleet elements present, but not always the same number or types of ships. Again, many of these will be in port at any given time, at various states of readiness.
Imperial and system fleets frequently run joint training exercises, since they'll need to coordinate closely during wartime. These exercises are usually conducted far from the mainworld to avoid interactions with civilian traffic. The volume in which exercises are occurring is off limits to civilian traffic; mainworld traffic control will steer ships away, and any civilian ship with a vector taking it in that direction will draw warning comm, followed by lots of unfriendly attention if the warning isn't heeded.