What sort of courses should I take before transferring?

I plan on transferring after taking a year of college at my local state university. I’ve researched what universities look for in transfer applicants and what I’ve gotten was “challenging courses.” With this being said, are there any particular courses you would recommend for my first year of college that would count as “challenging”? All I know for certain is that I plan on taking Calculus 1. Additionally, should I take more than 4 classes (semester system)? I know some people do but some don’t. Thank you for your help!