The TOEFL tests your language skills. Study products for the TOEFL focus primarily on explaining the format of the test and helping you learn key words, but understanding the format of the test will not suffice to get a good score.
I recommend beginning your study by taking a practice test. If you get less than 60% of the questions right, you probably need to work on your language skills before beginning you TOEFL studies. You can read more about this on our blog.
Most schools require a minimum score. As you begin your studies, it's important to know what your minimum score needs to be. This varies from school to school, so be sure to look up your program's requirements.
Once you have evaluated your starting level and end goal, I recommend using a pre-made study schedule to begin your studies. On our blog, you'll find two-week, one-month, and two-month schedules. You should consider how much time you have to devote to studying each day and how much improvement you need to make before deciding how long to study.
If you decide not to follow a schedule, start working your way through each of the lesson videos, and spend some time each day studying vocabulary and doing practice problems.
On top of the lesson videos and practice materials, you should use English as much as possible. This blog post offers some suggestions for English resources.
In short, to prepare for the TOEFL, you should use English every day :)