For most young professionals, your 20s are the years when you (finally!) start making some money. But, they’re also the years when, if you aren’t careful, you can make some money mistakes—ones that can (literally) cost you.

But staying on top of your finances is far from impossible. We’ve outlined four of the most common money blunders you might be tempted to make and how you can dodge them—and set yourself up for financial success in your 20s and beyond.

1. Credit Card Craze

Many recent grads think they can charge what they need or want now, then pay it off later, once they’re making more money. Problem is, paying off credit card debt is always harder than you think it’s going to be, and in the meantime, those high-interest cards and large balances can lower your credit score.

To prevent getting into more debt than you can handle, stick to only one or two good credit cards, and keep your balances below one-third of the available limit (or ideally, at zero). If you’re already overwhelmed by your credit card balances? Take control now. Rather than signing up for another card to get more credit, call your current card issuer and ask for an increase in your limit or a reduction in your interest rate. Then, lay each card you own out in front of you, record their balances and interest rates on a sheet of paper, and set up a strategy to pay them down with CNNMoney’s debt reduction planner.

If you can, set a deadline for your financial goals (i.e., I want to pay my cards off in two years so I can buy a new car). Even if all you can do is stop putting more on the cards while you’re making your minimum payments, stick with it!

2. Skipping Student Loan Bills

The average college grad amasses $25,000 in student loans—and wonders if it was worth it. Well, it was! A 25-year study from the U.S. Census Bureau estimates that people with a college degree will earn $2.1 million over the course of their lives, compared to the $1.2 million their high school graduate counterparts will make.

That said, many recent grads find themselves burdened by student loan debt on their entry-level (or non-existent) salaries and falling behind on their payments, which is a big problem. Going into forbearance or default on student loans slashes your credit score—and can even prevent you from getting a job (some employers run a credit check pre-hire).

To avoid this, make some smart moves: Consolidate your loans if you have any at variable interest rates, and set up an automatic draft from your checking account to make sure that the payment is taken care of each month (with federal loans, this will save you 0.25% on your interest rate). If you’re out of work or having trouble making your payments, talk to a loan representative about your repayment plan options.

3. Late Pay Laziness

I know it’s tough to stay on top of everything while you’re working like crazy, but don’t allow yourself to get into laziness mode with your bills—late fees are a totally unnecessary and preventable expense! And unfortunately, missing your due dates is a cycle you’ll struggle to get out of—you make one late payment, you get charged a fee, you fall behind the next month because you can’t pay the bill and the fee, repeat.

If you’re not paying your bills because you don’t have the money, start by setting up a budget so you can weed out any unnecessary expenses. Then, make sure the bills are always paid on time by setting up automatic drafts through your service providers or with your bank’s automatic bill pay. For bills that aren’t online (like your rent), set up calendar alerts to keep you from overlooking a due date. You can also have your bank or websites like Mint.com send you reminder emails.

4. The Travel Bug

I’m going to burst your bubble with this one, but it’s for your financial best! Traveling can get expensive, and it’s not a good reason to take on massive debt. I learned that the hard way: When I got back from studying abroad in Europe, I had racked up almost $3,000 in credit card debt. Yes, the experience was worth every penny, but it took me three years to pay off just three months out of the country!

While you don’t have to ban trips and vacations altogether, you should plan and budget for them wisely. If your trip is going to cost 10% or more of your annual salary, save for it: Open a separate savings account and have 10% of your paycheck automatically deposited there.

Also, be flexible on your plans—and look for easy ways to save money. Do you really need to go so far away (or stay at that five-star resort) to have the best experience? Look for up-and-coming budget destinations, snag deals on Groupon or LivingSocial, or visit places closer to home to minimize the largest cost factors of gas and airfare. Browse your Facebook friends to see if they’ve moved somewhere you want to visit (and would let you crash for a few days). No friends at your dream destination? Check out Couchsurfing for willing hosts.

Lastly, plan a trip for February or March to save on rates. Added bonus: Your boss will be happy when you’re willing to work the summer months, when all your co-workers are on their (more expensive!) vacations.

What have you found to be your main money temptations? Do you have any tips for how you’ve avoided these (and other) mistakes?

Photo courtesy of Ken Teegardin.