Do you have any advice on study skills for challenging courses?

Sometimes it's simply a matter of "seeing it the right way"--for example, picturing the unit circle with a triangle inside, whose side-lengths give the values of sine, cosine, tangent, etc., via simple ratios. (Or in my case, a math teacher who regularly stood with his arms pointing at different angles to help emphasize the relationships between angles on the unit circle and their trigonometric values.) If that's the case, then a study group like Theresa suggested, or a tutor, or even some YouTube videos such as those by Khan Academy, might be all you need for things to click.

It's also possible that math, or some parts of it, will always be a little more difficult for you (i.e., it's not simply a matter of seeing it from the right viewpoint), but that just means it will take more effort to do well in it. If there's one key lesson I learned as a teaching assistant in college courses, it's that hard work is far more valuable in the long run than native ability. Those students who were willing to put in the needed work--homework problems, sample test questions, etc.--invariably did well in the end, whereas the "natural genius" types at some point reached the end of their native abilities and started to fall behind, thanks to not having learned the necessary work habits along the way.

In my own college years, even though I had an aptitude for math (and majored in it), there was one subfield that just never clicked for me--probably because it was too abstract to be amenable to pictures, and I very much depended on being able to visualize the concepts to truly understand them. But I worked very hard in that class and kept plugging away at the homework problems, and I got decent grades for the entire year. Nevertheless, there are aspects of group theory that I've never been comfortable with, and I find it frustrating to this day. :-)