Short answer: every 3,000 to 5,000 miles or 3 - 6 months depending on the type of driving you do.
Long answer: When to change your oil varies with driving habits & type of vehicle. I’m assuming we share the goal to minimize the need for major auto repairs. If you’re driving 20 miles one way to work & 15 of those miles are on the highway, most vehicles should have the oil changed every 5000 miles. If you’re like me, drive 8 miles to work, never go more than 2 miles without stopping, most vehicles should have the oil changed every 3000 miles or every 3-4 months. If you ride the bus to work and only drive your car to run a few errands on the weekend, that is the hardest type of driving on an engine. You may need to change your vehicles oil every 3-6 months regardless of the mileage.