Deloitte chief executive Joe Echevarria overcame plenty of obstacles early in his career. He says you can, too. Here's how.

Joe Echevarria, CEO of Deloitte

FORTUNE -- No doubt about it, the current job market is no walk on the beach for anyone just graduating from college. Companies plan to hire just 2% more grads than last year, says the National Association of Colleges and Employers, a startling drop from the 13% increase those same employers projected last fall. And this year's fresh crop of degree holders will have to compete with the roughly 40% of the class of 2012 who are still underemployed or out of work.

Even so, Joe Echevarria believes success is within reach of anyone who wants it badly enough. He speaks from experience: After growing up poor in a single-parent home in New York City's South Bronx, Echevarria, who is Puerto Rican, faced a tougher struggle than most. Since 2011, he has been CEO of global consulting and audit giant Deloitte, No. 47 on Fortune's list of the Best Companies to Work For. This year the company will hire about 9,000 new grads. In a recent conversation, Echevarria recalled the early years of his career and offered advice on getting ahead against long odds.

Fortune: What was your first job out of college, and how did you get it?

Echevarria: I went from being an auto mechanic during the summers in the Bronx to getting hired as an auditor at Haskins & Sells [which later merged with Deloitte] when I graduated from the University of Miami, where I had gone on a scholarship. Back then, to get an interview with a Big 8 firm — it's now the Big 4 — you were supposed to have a 3.5 GPA. But, because I went to a not-so-great school — it was nicknamed Suntan U. — I had to have a 3.8. So I did that. I was at the top of my class in accounting, so they couldn't find a reason not to interview me, in spite of my rough edges.

MORE: A $100 million plan to save cities from the next Sandy

What rough edges?

I had a big mustache and bad hair. Also, I had two suits, one brown and the other green polyester. I had no social graces, either — I didn't know where the bread plate goes on a table, had never drunk coffee out of a cup with a saucer. It took me a long time to realize that these things matter in the corporate world. No one was willing to tell me.

Eventually I noticed that everybody else had more than two suits, and nobody wore brown or polyester. But because of these things, however superficial they might seem, I kept getting evaluations that said I had "low potential." Nobody thought I would ever get promoted. Also, I was paid less than anybody else in the [auditor training program]. But I caught up.

How did you do that?

Well, first, I figured out what successful people in the firm were doing. I looked at them and analyzed how they got there, and I tried my best to do the same. Then, I worked very, very hard. I worked harder than everybody else. And third, I had a boss, a Hispanic woman, who gave me good advice. Right before I left on vacation, she said to me, "You're coming back without that mustache. You will never make it into management if you look like the Frito Bandito." I had never realized that was holding me back. She is still my mentor to this day. I've been at the firm 35 years, she's been here 40. I call her my "mom" in the company.

What advice do you have for new grads now, or for anyone who wants to succeed at a big company?

First, you have to outwork everyone else. If you don't, talent will not help you. In this difficult job market, new grads may even have to work for free for a little while, in order to get a foot in the door. Find somewhere you really want to work and prove yourself by working hard and doing a great job, and I guarantee you that they will find a way to hire you and pay you.

I would also recommend reading a lot. Read everything you can get your hands on, because you'll always learn something you can use. One thing that helped me early on was a little book called It's Not How Good You Are, It's How Good You Want to Be [by British ad man Paul Arden]. It's really for salespeople, but you can apply a lot of the wisdom in it to yourself. I still pick it up and read it now and then.

MORE: New York City's Christine Quinn wants no B.S.

Third, find a mentor who will be honest with you about your shortcomings and show you your blind spots, because everyone has them. If you walk through my old neighborhood in the South Bronx even today, half the men have these big mustaches, so I just never thought twice about it until my "mom" told me to get rid of it.

What does Deloitte look for in hiring new grads?

Altogether, we hire about 18,000 people each year, about half new grads and half experienced professionals, and we go through about 500,000 resumes and applications every year to find those 18,000. Beyond the basic credentials and competencies, we're looking for people who stand out. If you are a passionate person, that will stand out. If you are positive and enthusiastic and other people want to be around you, that will stand out.

And do you finish what you start? It sounds basic, but so many people start out strong on something and then don't follow through. We also look for people who care about people. Those qualities are the difference-makers, and they will always be the difference-makers, between an okay candidate and a great candidate.

As a member of an ethnic minority, do you have any special advice for new grads who are also minorities?

I would say this: Whatever disadvantages you may have faced up to now, because of your ethnicity, that is all about to change. The fact is that there are not enough talented minority managers, or management-track entry-level people, to reflect the changing demographics of the U.S. population, which by 2050 will be more than half "minorities." So you are in demand. Deloitte has been steadily increasing recruitment of black and Latino talent, because if we don't get our share of it now, we won't be in a good place in the years ahead.