The best way to care for your tires to ensure that you get the longest life out of them is to regularly inspect them for any uneven wear and tire, low tire pressure, and tread depth. Often times, we only focus on our tires when there is an emergency, like a flat, but you can get a lot more miles out of your tires--and better gas mileage--if you regularly have your tires rotated, balanced, and properly inflated. Uneven tire wear means you might have to replace some tires before others and also could mean that your car isn't performing as well as it should.
Weight on your front and rear tires will inevitably be different, which causes your front and rear tires to wear at different rates. But swapping them (on cars with the same size tires for the front and back) could be an easy and cheap way to extend the life of all of your tires. Additionally, making sure your passenger side and driver side tires wear evenly could help you maintain a smooth performance of your vehicle.
In some cases, maybe you favor right turns vs. left turns. In that case, you'll notice an uneven wear and tear on your tires. Therefore, tire rotation becomes even more necessary in these cases and you'll be able to identify a need for a rotation when you inspect your tires for uneven wear and tar.
Depending on your vehicle, your manufacturer may recommend different tire rotation intervals (due to weight and size), but in general, it'd be great to do every 8,000 miles. You'll typically want to move the back wheels to the front.
In any case, this is a much more cost-effective service than having to replace the tires prematurely.