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There are some basic rules in personal finance that are so vital for success that they pertain to everyone, no matter your age. Tenets like spending within your means and never carrying a balance on a high-interest credit card apply across the board. But how can you know if you're making any serious financial slip-ups for your current age?

Here are some tips to avoid costly money mistakes when you're in your 20s, 30s, and 40s. I'll also share a secret method you can use to learn about money and wealth (or about any subject, for that matter) that's quick, easy, and maybe even kind of fun!

20-Somethings: The Three Mistakes to Watch Out For

If you're in your twenties, it's likely that you're staying in school longer, putting off moving out of your parents' home, or delaying marriage and children. You have high expectations for a career that pays well, suits your lifestyle, and inspires you get out of bed each morning. Dramatically improve your financial health by avoiding these three serious money mistakes that can come back to bite you later on:

Accumulating credit-card debt. Now that you're a working adult, you might think that you're entitled to lots of new clothes, nights out on the town, and vacations. The problem is that financing a lifestyle that you can't afford using a credit card is a terrible financial move. It's a grim mistake that sticks with you for years and will only get worse as interest accrues each month that you don't pay off the balance.

Now that you're a working adult, you might think that you're entitled to lots of new clothes, nights out on the town, and vacations. The problem is that financing a lifestyle that you can't afford using a credit card is a terrible financial move. It's a grim mistake that sticks with you for years and will only get worse as interest accrues each month that you don't pay off the balance. Ditching participation in a 401(k). You might be hesitant to start contributing to a workplace retirement plan (like a 401(k) or a 403(b)) if you aren't sure how long you're going to stay in your job, but letting that stop you from contributing — especially when you're offered free matching funds — is a big mistake. Contribute 10% to 15% of your income and then roll it over into an IRA or a retirement plan at your new employer after you leave the job. No one wants to feel behind; start contributing today and you won't wake up in your 30s with big financial regrets.

You might be hesitant to start contributing to a workplace retirement plan (like a 401(k) or a 403(b)) if you aren't sure how long you're going to stay in your job, but letting that stop you from contributing — especially when you're offered free matching funds — is a big mistake. Contribute 10% to 15% of your income and then roll it over into an IRA or a retirement plan at your new employer after you leave the job. No one wants to feel behind; start contributing today and you won't wake up in your 30s with big financial regrets. Not seeking professional advice. Don't think that you have to be self-sufficient when it comes to handling your money. Get help from a professional — like a Registered Investment Advisor, a financial planner, or a financial coach — to figure out how to set and achieve your unique goals.

30-Somethings: The Three Mistakes to Watch Out For

If you're past 30, you might be starting a family, moving into a larger home, and climbing up a career ladder. During this life stage you need to stay focused on your goals and make sure you can provide for your family if you lose your job or business. Shore up your financial defenses by avoiding these three financial oversights:

Forgetting about an emergency fund. Add up your monthly living expenses and multiply that number by six to figure the minimum amount you should keep on hand in an FDIC-insured savings account. Depending on your job stability, industry, and family situation, you might need to have a year or more of emergency savings stashed away. Doing this will ensure you're protected in case something unexpected arises (like an illness or job loss) and that you'll be able to keep your life plans on track.

Add up your monthly living expenses and multiply that number by six to figure the minimum amount you should keep on hand in an FDIC-insured savings account. Depending on your job stability, industry, and family situation, you might need to have a year or more of emergency savings stashed away. Doing this will ensure you're protected in case something unexpected arises (like an illness or job loss) and that you'll be able to keep your life plans on track. Skimping on retirement savings. As you begin to earn more money, it might be tempting to spend more on fun trips, fancy cars, and designer clothes. Treating your extra money carelessly and not increasing your contributions to a workplace retirement plan, an IRA, or to both is a mistake. You might also have higher expenses now, but you still need to carve out enough from your budget to keep long-term goals like retirement and paying for a child's education on track.

As you begin to earn more money, it might be tempting to spend more on fun trips, fancy cars, and designer clothes. Treating your extra money carelessly and not increasing your contributions to a workplace retirement plan, an IRA, or to both is a mistake. You might also have higher expenses now, but you still need to carve out enough from your budget to keep long-term goals like retirement and paying for a child's education on track. Not being properly insured. Having enough of the right kinds of insurance is an easy way to reduce risk and ensure that you and your family can get through unexpected hardships like an illness, accident, or death. Insurance doesn't help you build wealth, but it certainly helps you protect it.

40-Somethings: The Three Mistakes to Watch Out For

If you're a parent in your 40s, you might be looking forward to launching your kids out of the house, doing a happy dance, and refocusing on your own financial needs. This life stage is a great time to simplify your finances and reevaluate your retirement dreams. Don't let these 3 money mistakes trip you up:

Failing to focus on retirement. Though you probably have about two decades to go before retirement, you're getting closer and need to take it more seriously. Enter your information into a retirement calculator at sites like aarp.org and dinkytown.com to make sure you're putting enough money aside each month.

Though you probably have about two decades to go before retirement, you're getting closer and need to take it more seriously. Enter your information into a retirement calculator at sites like aarp.org and dinkytown.com to make sure you're putting enough money aside each month. Not eliminating debt. In addition to saving for retirement, free up as much discretionary income as possible to send extra payments to your debt. Getting rid of debt sooner rather than later saves a huge amount of interest and allows you to squirrel away even more for retirement during your 40s and 50s.

In addition to saving for retirement, free up as much discretionary income as possible to send extra payments to your debt. Getting rid of debt sooner rather than later saves a huge amount of interest and allows you to squirrel away even more for retirement during your 40s and 50s. Ignoring “teachable” moments. Instead of allowing older children to drain your bank account, teach them how to earn and manage their own money. Help them create a job resume, open a bank account, stick to a budget, set savings goals, and invest for retirement. Even minors can open up and contribute to an IRA as soon as they get their first part-time job!

A Secret to Learning About Money and Wealth

I'm sure you realize that these tips just scratch the surface and that there's a whole lot more to know about making smart moves with your money. Taking the time to learn about money and wealth pays off whether you're a young student, a grandparent, or somewhere in between.

Here's my secret for the best way to learn about money: Make getting the information fit into your lifestyle.

If you love being on the computer, subscribe to Get Rich Slowly so you never miss a post. If you like reading during your lunch break or while you travel, regularly read personal-finance books, such as J.D.'s Your Money: The Missing Manual or my own Money Girl's Smart Moves to Grow Rich. (You can download two free chapters of my book at SmartMovesToGrowRich.com.) If you spend way too much time in the car or don't want to get chatty during your pedicure, listen to a money podcast. If you need to be entertained while you're on the…in the…you know — take a money magazine with you.

You get the idea. See where you have time to squeeze in 15 or 30 minutes of reading or listening about money and you'll be amazed at how easy it is to take your financial game to a new level, build wealth, and get rich slowly.