TIP: Keyboard modifiers in Free Transform

When you're using Free Transform, use these keys to change the way that it operates when you drag on a handle:

Shift: Keeps the transformation proportional
Option (PC: Alt) Transforms from the center outwards
Command (PC: Control): Transforms only the one handle you click on
Command Shift (PC: Control Shift): Skews the area you're transforming
Command Option Shift (PC: Control Alt Shift): Creates perspective
Move your mouse just outside the handles to get the rotation cursor, and
Use Shift to rotate in 15 degree increments

from Photoshop Finishing Touches