In recent years, internships have gone from nice-to-have-on-a-resume to absolutely critical.

Employers in the United States today go on to hire about 50 per cent of their interns as full-time workers, according to the Collegiate Employment Research Institute at Michigan State University.

And the share is growing every year in industries like construction, consulting, accounting and scientific services.

This new emphasis has upended the traditional recruiting calendar on campuses nationwide. With more companies drawing from their intern pools, recruiters have shifted their attention from hiring soon-to-graduate seniors to scoping out juniors, even as early as the fall term, for summer internships.

Postings for internships now make up a significant proportion of the overall entry-level job openings in engineering, graphic design, communications, marketing and information technology, according to Burning Glass Technologies, a data analytics company that studies the job market.

"There was a time when 50 employers came to recruit for interns," said University of Pennsylvania director of career services Patricia Rose. "Now we have 180. They want to wrap up talent before anyone else."

No one wants to be the first full-time employer of new college graduates any more.

Internships are "a really smart way to recruit", said Mr Adam Ward, head of recruiting at Pinterest, where about a third of interns are hired in permanent jobs. "It's all about trying before you buy."

So how do students make the most of these short-term experiences? I asked three recent interns in different industries to share their advice.

START EARLY

Mr Matthew C. Pickett now works in the US State Department's public affairs office, where he had his first internship the summer before college.

"Having an internship or working as a teenager gives you a sense of how an office functions; you learn how to network, and you see what different jobs are like," he said.

"I also learnt how to navigate in a group environment with people of all ages, not just my peers."

He returned to the department every summer, building up the skills that got him hired after graduating from George Mason University in 2015 with a degree in history.

SELL YOURSELF

In her junior year, Ms Megan Mullen managed to meet most of the 70 employers attending a career fair at Indiana University.

"You have 15 seconds to give an elevator pitch," she said. "You can't just hand them a resume and expect them to read it. They won't."

Her advice: "Don't just repeat your resume. Tell them a story, bring up experiences that aren't on your resume and tie together your skills and experiences to show how you can help them. Getting an internship is a sales job."

That day, Visa invited Ms Mullen for an interview. She got the internship.

Once you're there, she said, "don't be afraid to tell people your career goals and what you want to do". "They want to support you. Speak up. But also be careful what you say," she added.

"I was unsure if I wanted to live in California", where there was a full-time job with Visa.

"I mentioned that uncertainty to my manager, who misconstrued it as me not wanting any offer that would place me in California."

DO YOUR RESEARCH

Firms hire interns who show genuine interest in their businesses, not those who are just looking for a summer job, said Ms Lauren L. Morrison.

She spent hours researching Ford before the carmaker held its information session at Florida A&M University, where she was majoring in business administration.

"By then, I knew what they were trying to do to improve customer service," she said.

"During a conversation with the recruiter, I was able to connect the company strategy to what I learnt in my business classes."

Ms Morrison landed a marketing stint with Ford and was the only intern in the Florida office.

"I was laser-focused," she said. "I sat at my desk every day until my mentor told me that if I did just that for the rest of the summer, I'd be just a number in a large company.

"I went around and asked people what they were working on and if they needed help. I got another project that way, where I had to present to the regional managers at the end of the summer."

Her managers were impressed.

Ford offers jobs to about half its 600 interns every year.

Ms Morrison was one of those hired.

NYTIMES

• Jeffrey J. Selingo is author of There Is Life After College: What Parents And Students Should Know About Navigating School To Prepare For The Jobs Of Tomorrow.