I'll try to keep this short & sweet:
(on my fifth and final year of undergraduate engineering now

)
-Before doing FIRST during college; ask yourself "how will FIRST help me accomplish my career/life goals?"
-Pick the ONE aspect of FIRST that will MOST help you gain a competitive edge in your career/life goals (mentoring, design, machining, writing, project management, procurement, fund raising, leadership, etc...)
-Make sure that ONE aspect is a lot less involved than what you think you could handle.
-Do that one aspect well.
You may change that one aspect from year to year, according to how your career/life goals change, but what I found out in college is:
FIRST can help you advance your skills & knowledge base.
FIRST can help you discover your own interests & expertise.
FIRST can lead you to job offers.
FIRST can make you stressed out beyond belief and distract you from classes!
So basically, if you must do FIRST (and I do recommend staying involved), do one small thing, do it WELL (people will notice that), and spend the rest of your time concentrating on classes.
The ONLY reason I did so much with FIRST during my undergraduate career is because I was working at internships between the months of January-June for 2004, 2005, & 2006. Had I been involved with classes during the winter months I would have accomplished far less.
All in all... if you're obsessed with FIRST, do an internship during build season

.