At country airports, you might find there isn't an obvious spot to do runups, so sometimes it's just easiest to do it where you're parked. If you do though,
1) Check what's behind you. If there is another aircraft, move to somewhere where your prop wash isn't going to kick stones up onto someones plane.
2) If there is a decent amount of wind, at least make some effort to point the nose into wind.
3) If you're going to do your runups where you're parked, during your walk around, have a quick look on the ground beneath the prop. If there are loose stones, kick them out of the way (or brush them out of the way of you're lucky enough to have a dustpan in the plane)