On Graduation Day you're probably giddy from people telling you: "Congratulations!" and "Seize the day!"

Here's what they should tell you: Dream big about many things, including your finances.

Paying your bills is part of saving the world. In fact, the better you are at handling your money, the more of it you'll have to put toward fun, travel, retirement, student loans or your next big game-changing idea.

If you're heading to work on Wall Street or Silicon Valley's upper echelons, good for you. Save your bonuses in the early years and you'll be fine. Everyone else, read on.

I graduated from college just over a decade ago. At the time, I recall listening to an NPR story about a woman in her early 30s. She did Teach for America after graduating and decided to stay in education. She wanted to make a difference.

Related: From Millennial to millioniare in 5 steps

By her 30s, she still felt passionate about her students, but she sounded distraught when discussing money. She was still driving a used car, living with roommates and vacationing at nearby beaches and parks. Her salary had grown little. In contrast, many of her friends were thriving financially.

I've seen the same progression in my own life. While everyone is telling you to live it up in your 20s, plenty of your peers will also be (quietly) getting their finances in order.

Somewhere around age 30, your friends will start buying houses. One person I know even has a second home already. And yes, soon you'll probably find yourself talking about 401(k) balances over summer drinks. A friend who works at Google (GOOGL) actually told me he's worried because he only has about $100,000 so far in his retirement account.

Will you have enough to retire? Check CNNMoney's retirement calculator

So what the heck do you do if you're heading for a career in government, journalism, nonprofit or something else with a "modest" salary? Here's what I've learned:

1) Cheap housing is your new BFF. You can spend a ridiculous amount of time building fancy budget spreedsheets or reading blogs and books about money. But the reality for most recent grads is that your rent payment will determine whether you financially flourish or flunk.

It's most people's biggest expense -- by far. I now live in New York where the real estate agents advise people to keep their rent (or mortgage) payments below 33% of your pay. Here's a better tip: keep your rent below 25% of your salary. If you're making about $50,000 a year, you save roughly $4,000 by opting for the cheaper place.

I moved four times my first year out of school. I didn't sign any leases. Those come with upfront costs ("security deposits"). Instead, I rented rooms in people's houses. Friends thought I was nuts, but I was able to keep my expenses low (I even paid rent week to week in many places) and I didn't waste my time (or money) buying furniture, let alone moving it.

Related: Most and least affordable rental markets for new grads

I quickly learned that while it's fun living with a bunch of other millennials, there's also this whole market of Baby Boomers (often widows or divorcees) who also rent rooms. Their homes tend to be really nice and they will sometimes make you breakfast. This tactic only cost me about $800 a month in London while many friends were paying $1,500+. That left me with a lot more money to save, invest and have fun with.

2) Start your own money club. Parents are the first people many 20-somethings call for financial advice. Sure, they have experience, but keep in mind: they tend not to be as savvy on all the mobile app resources available today. And they probably haven't lived on that $40,000-a-year starting salary in a very long time.

An even better move is to talk money with your peers. An alum from my college started a private Facebook (FB) group to talk finances. It's quickly become one of my best resources. People post about everything from the best credit card reward program to whether to buy a socially responsible investment fund. It's honest feedback from people who have messed up and don't want you to as well.

Share your story: What are YOUR money regrets?

If you've just graduated, you have a great network of friends who are moving all over the nation (and probably the world). Leverage that knowledge. If you want an even bigger circle, join an investing or financial club. There are Meetup groups and online communities like startups Openfolio and Stocktwits where people share investing advice. I'm a big fan of Reddit's "Moronic Monday" threads. Ask anything. Get free advice.

3) Forget "buy low, sell high." Just start early. Unless you start the next Facebook, the only way you're ever going to be a millionaire is if you save a lot AND invest in the stock market. The key is to start early.

Ask your friends and family. At CNNMoney, we've heard from a lot of people about how their grandma or great aunt (interestingly, it's often women) bought Disney (DIS) or AT&T (T) stock in the 1970s or 1980s. Today that $1,000 invested Disney is worth an insane $100,000 or more.

I sat through several talks in college on the power of compound investing, but it hit home a lot more when I started hearing about and meeting some of these shrewd grandmas who saved money in coffee cans and sent it off occasionally to buy stock. If they can do it, you can too.

Related: Real people are getting rich off Apple stock

The easiest way to get going is to sign up for your company's 401(k) retirement plan. Even if you just contribute 2 or 3% of your annual salary, it will start to add up. Many companies match a portion of whatever you put in. That's about as close to "free money" as you're ever going to get in adult life and could easily be worth $1,000 to $2,000 a year.

I started my working life in London where there aren't 401(k) plans. I really regret not opening an IRA (individual retirement account) and doing it myself. It's harder, but it's all about getting going early. Instead, I didn't start my 401(k) until I was 27. Some of my really smart friends actually have both a 401(k) and an IRA where they put EXTRA savings.

Places like Vanguard make it really easy to open an IRA and buy a low-cost index fund that tracks the S&P 500. If you're really on a budget, you can use a neat new app called Acorns that allows you to invest just a few dollars at a time.

Related: This app has helped Millennials save millions

4) Pay off those credit cards. I missed a credit card payment once. By accident. I missed it by one day, and I owed $25. That was my whole meal budget for a day or two. It hurt. My friends who are the most behind at age 30 are the ones who ended up with a lot of credit card debt. Much like student loans, it takes a big chunk of your monthly wages to pay it off.

That said, you want to make sure you have at least one credit card. When you apply for an apartment or mortgage (trust me, it will happen by age 30 for some people!), one of the first things the bank or landlord does is look up your credit score.

That score is based partly on how much credit you have available to you as well as whether or you pay your bills on time. If you don't have a credit card, you won't have the debt, but you also won't be able to show that a credit card company was willing to lend you $10,000 or $20,000.

Earning that college or grad school degree is empowering, but buying your first home, paying off your student loans or simply having enough money to take your parents out to dinner (instead of vice versa) is quite the accomplishment.

Heather Long is CNNMoney's Markets & Investing editor. She is a graduate of Wellesley College and Oxford University.