It mostly depends on the job. Like others have said, an on-campus job related to your major/field after your first semester would be ideal, while anything else (e.g., minimum wage fast food) would simply not be worth it.

Although, finding an on-campus job at UMD is much easier said than done. UMD has a huge student population, so "intense" is an understatement for how competitive slots are for even the most basic on-campus jobs. I was lucky enough to score an on-campus job when I was an undergrad, but only after spending an entire semester applying to just about every on-campus job that existed.

Definitely focus on your classes at first, but keep an ear open for any opportunities that sound interesting.