1. Buy a used car.
Actually, this was DH's mistake (although he won't admit it because he has always, always wanted to be the first to own a car after years of hand-me-downs). After I figured out the cost in terms of how long I had to work (approximately one year), I decided never to buy a new car again. A newer used car will be just as good for thousands cheaper.
2. Never lend money to friends or family that you can't afford to never see again.
This was the most expensive lesson - to the tune of $5000. If I had to do it again, I would in a heartbeat (DH's parents furnace went out in November right after his dad went into the hospital for a triple bypass. They had just entered credit counseling and had no credit available. We found out that the ductwork was leaking carbon monoxide and fronted the $5000 for a completely new heating system). My mistake here was in expecting the money back, not in lending it. I carried around some bitterness for a few years at not seeing the cash (DH on the other hand, never expected it back). If you have the ability to help out, and you don't want to ruin a relationship, give a gift instead of a loan. If you can't afford to spare the cash, don't give the loan.
3. Don't buy a house just because it's cheaper than rent.
You can also substitute any number of reasons here for not buying a house, but in our case, it simply was cheaper than rent (by about $90). We were also newly married and completely uneducated. We bought a cheap house, poorly maintained, in a declining area. We also did not plan to stay in the area for more than 3 or 4 years. Somehow, after seven months on the market, we managed to get close to our asking price. This could have turned out much, much worse, but we walked away from it with a little more than our downpayment. I loved our house and, again, wouldn't change our decision, but it certainly gave me a new perspective on future housing and the right reasons to buy.
4. New clothes are usually not worth the price.
It took me years of shrinking, staining, and otherwise ruining expensive clothing that I had only worn once or twice to realize this. Of course, there are always going to be certain items that you have to buy new, but in general, 90% of my wardrobe comes from thrift stores, hand-me-downs, or garage sales. If I tire of an item, or ruin it, I have no guilt about getting rid of it.
5. Full price is usually negotiable.
Once I started trying, I found that you can get the price down on just about anything if you ask, bargain, or threaten to take your business elsewhere. I managed to find this out by accident one day when I was shocked by the price of a car repair. Instead of authorizing the work, I told the mechanic to hold off while I checked around for prices. Lo and behold, about 15 minutes later, the mechanic called me back with a significant discount, saying that he "happened" to find a part cheaper somewhere. A little light bulb went off in my head, and I now check around before any major purchase, including searching the Internet for coupons for anything from coffee, restaurants, photo processing, or oil changes.
6. Invest as early as you can.
DH and I started early, by most standards (age 25). However, in the few years leading up to our investing start, we were sitting on $10k+ in the bank. If we had just started investing some of that a little earlier...
7. If something is wrong, complain.
If you are not getting a service that you paid for, or are getting overcharged for it, call the company. If you do not get a favorable response (and feel you are being wronged), take it one step higher until you get what you need. The company president, the Better Business Bureau, even the local news can be powerful catalysts to right a wrong. I started heeding this advice several years ago, once getting a $50 credit and another time getting out of a contract that was misrepresented to us. However, I missed many opportunities to get what I deserved before I found my voice.
8. A fancy college is not always worth the price.
I'm not going to make a blanket statement here, but for me, I do not think a private four year college gave me any more of a head start than a community college would have. I still remember this mistake every month when I pay off my student loan (which would have been done about 4 years earlier had I went to a community college for two years, then transferred).
9. And, finally, not money related (unless you count him as the best investment I ever made!), don't overlook your best friend when looking for love.
This would have been my biggest mistake ever, had DH not been so darn persistent. He was a good friend and wanted it to be more, but I could only see him as "just a friend". Sometimes what you really need is right under your nose
9 things I have learned from making mistakes
1. Buy a used car.