Understand the math first
The more credits you already have, the more your GPA resists change. A single A has a big effect in your first semester and a small one by your senior year. Use a GPA calculator to model exactly how a target semester would move your cumulative number before you set expectations.
Prioritize high-credit courses
Because GPA is credit-weighted, doing well in a 4-credit course moves your average more than the same grade in a 1-credit course. Put your best effort where the credits (and your struggles) are concentrated.
Retake courses and use grade replacement
Many schools let you retake a course and replace the original grade in your GPA. This is one of the fastest ways to recover from a low grade — check your school's grade-replacement policy for the rules.