We often resize objects to fit into a certain size. And such operation has a short cut - Ctrl-T (free transformation). But sometimes we need an additional tweak of the perspective. There is a separate menu item to do so: Edit, Transform, Perspective. This tool is useful, though most of the time something simpler would suffice. And that's a neat trick in Ctrl-T mode - while holding Ctrl key drag any of the corners to freely adjust the shape.
Note: You may drag the sides as well, and to lock the movement only to one of the directions hold Ctrl and Shift.
Extra: To ensure that your lines are straight in the picture (while adjusting perspective) press Ctrl-' to reveal the grid (press once more to hide it).