At what level? Does the course has assigned or recommended texts?
At the most introductory level there is Basic Training in Mathematics: A Fitness Program for Science Students by R. Shankar,
https://www.amazon.com/dp/0306450356/?tag=pfamazon01-20.
I, too, recommend
https://www.amazon.com/dp/0471198269/?tag=pfamazon01-20 by Boas, which is a standard text for junior-level mathematical method courses. I wasn't very familiar with this book until I used as the text for a course that I taught a few years ago
https://www.amazon.com/dp/0120598760/?tag=pfamazon01-20 by Arfken and Weber is a standard text for grad-level (or possibly senior-level) mathematical methods courses.