Besides hitting a curb or pothole, etc., misalignment can often be so subtle that it may not be noticeable. Including tire alignment checks (and corrections as needed) in your regular preventative maintenance routine is important. For an exact answer on how often it should be done, look in your vehicle’s owner manual for the recommended alignment schedule from the manufacturer.
Generally, you should have your alignment checked once a year, at a minimum. A good habit to get into is to have it checked during every other oil change or tire rotation. You also always want to have it done when new tires are installed. If you have a collision, hit a large pothole, or have similar situations, you should have your wheel alignment checked ASAP.
Catching any misalignments early will help ensure your vehicle stays in the safest driving condition. It also prevents you from needing to replace tires more frequently, spend more money on gas, or make costly steering system repairs.