One way is to talk about yourself:
“I need the three credits to graduate.”
“I really want a job in that field.”
“I need experience for my resume.”
The thing is, most people don’t care about your needs. Employers certainly don’t. They care about what you can do. They care about how you can help. Most of all, they care about why you’re asking in the first place.
Perhaps a better way is to focus on what the other person needs. Even better, focus on a shared vision of the future.