Tip 1: Level your horizon line. A slanted horizon plagues many an otherwise excellent landscape. Even with a tripod, it’s hard to tell by eye that you’ve got it right. Photoshop CS5 finally includes a tool for straightening as part of the Ruler tool. Find it by clicking and holding the eyedropper in the toolbar. Use the ruler to draw a line along the horizon where it should be straight—in this case, the water line. Then click the Straighten button in the Options bar at the top of the screen.