Practising or repeat learning is essential for success because when you are not preparing someone somewhere is studying, who have more chance of success. You should strive for deliberate practise where you knowingly and purposely repeat activity to improve performance. It involves attention, concentration, and reflection.
Besides talent, the intense practise for an extended period makes a person expert in the field. The difference in students performance is due to deliberate practice. A student needs to be motivated to improve his/her performance and continuously put an effort to become better. Use your pre-existing knowledge and review your performance to know what went wrong and what needs improvement.
There are two reliable ways to improve test score:
Genuine improvements in the subject knowledge to improve your abilities
Decrease anxiety, increased familiarity with format, and time management.
Practice tests make students familiar with what to expect in the tests, for example, questions types, and test format. Taking practice tests under time constraints similar to the live testing situation will help the students to become familiar with questions types and test format, test instructions and test-taking conditions.
The practice may not make you perfect, but it will certainly improve your abilities.
To know more about the relationship between practice and performance, read the following journal article:
The Role of Deliberate Practice in the Acquisition of Expert Performance by K. Anders Ericsson, Ralf Th. Krampe, and Clemens Tesch Romer
https://projects.ict.usc.edu/itw/gel/EricssonDeliberatePracticePR93.PDF.