Do NOT be a card collector. Business card collectors have big books or binders of neatly organized business cards. Those books are usually worthless because the relationships aren’t nurtured properly, if at all.
If you are still in school, whether high school or college, and someone you look up to or who could be a future mentor gives you his or her business card, follow-up the next day.
And after the follow-up call or meeting, thank you cards still trump emails. Get out the pen and paper and connect!