Some common mistakes people make when planning for retirement are not saving enough, not investing properly, and not revisiting their plan as they get closer to retirement age. Not saving enough is a big mistake, as you will need a lot of money saved up to have a comfortable retirement. Not investing properly can also be a problem, as you want to make sure your money is working for you and not just sitting in a savings account. Finally, not revisiting your plan as you get closer to retirement age can be a mistake, as things can change and you may need to adjust your plan accordingly. It's important to stay flexible and be willing to make changes as needed.