It’s almost certain that you once had a test go badly. Whether that means you failed, or that you got a much lower score than you are used to depends on who you are and what your expectations are during a test. However, I would argue that the reason you had a bad test largely stems from the problem of not knowing where to start.
Indeed, this is problem that will often occur to me on tests. It’s not that I don’t know the general sort of thing I need to do in order to complete the problem. It’s that I’m unsure what my first steps should be.
The best method I’ve found to combat this is to try and find a general “rhythm” for solving problems. Typically, each class has different “types” of problems. In my calculus class, we had problems dealing with area and volume, we had constraint problems, and we had problems involving space curves. These are all different types of problems with their own normal routines. As such, a better way of studying than just memorizing formulas is to embed the pattern – or rhythm – of the problem into your mind. That means you always do your first step when you encounter this kind of problem. Then, the only thing you need to do is recognize what “kind” of problem you have, which is usually easier.
Once you are able to pick out the patterns of problems, it becomes a lot easier to know where to start and how to solve. Don’t reinvent the wheel. There’s a joke in physics about spherical cows (link), and how we try to tackle a bunch of our problems by reducing them into easier problems. This isn’t necessarily a bad way to tackle sets of problems. Try and figure out the common patterns between them, and use that to inform what your first step should be. This will help mitigate the “I didn’t even know where to start” problem in tests.