Understanding "prerequisites" for undergraduate research with a certain professor I'd like to do research with one of a few professors within a certain group in my (American) university's Computer Science department. I'm having some trouble contacting them, but I'd like to understand what I can do, as an undergraduate student, to increase my chances of getting research with one of the profs I am interested in.

The group they are in teaches only a few undergrad classes, which, as of next semester, I have completed all of. Yet I was, through a series of extremely unfortunate class schedules, unable to be taught by any of the professors I want to research with, although next semester I will be taught by their colleagues in the same group. I talked to a couple TAs and other profs, who said to "just get better at the research topics in question", although this seems like altogether unhelpful advice given the gap between a first year undergrad and a professor's research.

There are no classes that really delve into the exact research that the professors I would like to research with do, although the class I am taking next semester covers the basics of what the group is about.

What can I do to understand what the "prerequisites" for being a research assistant to the professors in question would be (beyond just "get better")?
The "prerequisites" are really going to depend on the field that your professors of interest are publishing in. Which will lead me to the next point: if you're interested in this field, read some publications from these professors or other professors/experts in this field, then stop by their office hours or talk to them and mention your interest in the field and what you can do to gain more knowledge.