First of all, I am an accountant at an insurance company. So I deal with daily financial transactions that are made and recording things for the financial statements. Well that's a simplified job description. There are many different types of accountants and the jobs can vary drastically.
I have tasks that need to be completed daily, weekly and monthly. Over time, I have just learned what these tasks are and know that they need to be done. I know what my daily tasks are so that's easy, I just go into work and do them every day. For everything else, I kind of schedule myself. I know what needs to be done each month and when it needs to be done by. I write them all in my calendar. Mostly this isn't a strict schedule, more of a guideline. It's basically a lot of time management and planning my own schedule.
Sometimes random things come up that take priority, and in most cases, my regular tasks aren't on a strict enough schedule and I can do them. Take yesterday for example, I basically didn't ever get to doing what I thought I was going to do. But that's ok. It's what keeps life interesting.