First make sure you understand why the formulas are like that, why things behave like they do, just try to have a general understanding of the topic. Don't just learn the formulas by heart, understand them! Try to even derive them on your own! If you'd like a great explanation of a physics, maths or any other science topic there's a great site called khan academy you should definitely check out! Highly recommended!<br />
But to become less error prone while solving the problems you have to practice a lot, which isn't a big deal once you understand it all.
The same way one learns anything: practice practice practice practice practice.
Do past papers. It's far easier to learn the test than the subject.
Why don't you ask a teacher ?
Yes, your teacher, what they are paid for. Good luck.