Whether you're new to inline skating or a seasoned veteran, there are at least three big things you should watch for when you're skating local roads and trails.
Tar snakes - These black, "snakey" looking lines of fresh tar can send you sprawling if you're not careful. While they're useful for patching up cracks in pavement to stop the cracks from getting worse, tar snakes are softer than pavement and can catch your skate wheel and suddenly stop your forward momentum leaving you off balance. Obviously it's best to avoid them altogether, but if you find yourself approaching these discouraging black lines just remember to skate perpendicularly across them (think at a right angle) and be extra cautious.
Trail debris - Leaves, sticks, pebbles... the miscellaneous debris you might encounter on a given road or trail can get stuck between your skate wheels and trip you up. The bigger the wheel, the easier it is to skate over the occasional twig without any trouble, but be on the lookout so you're not caught rolling over them unaware.
Other trail users - Speaking of being unaware, you might assume other folks walking, biking or skating in front or behind you are paying attention to their surroundings, but it's not always the case. Be watchful of your skate placement and how much space you're using, and always announce yourself when passing someone so you don't catch people - or the dogs they're walking - off guard. It's all too easy to tune out the world when you're skating without a partner, especially if you're plugged into your favorite music and settled into the rhythym of a great workout.
Lastly, and most importantly, always remember to enjoy your skate!