Money problems almost always fall into one of the following categories. If you can plan for these things, and practice some basic money-management skills, you will be able to avoid many money problems.
Not planning for emergencies- This is one of the biggest mistakes you can make, and it can lead to all kinds of money problems. The fact is, bad things happen to good people and bad people. You can't expect life to go perfectly, cars break down, people lose jobs and get sick, complications happen, appliances go out, even when they are almost brand new, etc. This means that if you do not have some cash set aside to deal with emergencies, you are going to be in a bind financially. Start an emergency savings account, not for things like a house or a car, but to deal with the emergencies that happen, such as job loss. Put a good amount in it, and work toward the goal of saving six month's worth of income.
Not budgeting- The next biggest mistake people make with money is not having a budget. You can't properly manage your money if you do not know where it is going, and where it should be going. Give each dollar you earn a job. This is what a budget is. It means that when you get paid, you know where each cent needs to go in order to provide for your needs, pay your bills, help you save, and have some fun out of life. It is how you stay out of debt, and meet your financial obligations without stress. Make a budget, and practice sticking to it.
Pretending things will work themselves out- Another big money mistake is not making any changes in your habits but believing that things will work out. You can hope for the best all day and pretend that things will work themselves out, but until you commit to practicing good money management skills you will not get the best. Stop being ignorant and leaving your financial situation to fate. Take control of your own financial destiny. You have to make good choices, and manage your money, it won't manage itself.
Money of your own- If you are a couple that shares financial responsibilities, like a married couple, one of the mistakes often made is that of not having any money individually. This is not to say that each member should have their own bank account, but they should have a set amount each month that is theirs to spend as they choose. This money will help control impulse shopping and over spending due to feeling like you do not have enough.
Secrets/denial- Another common couple money mistake is keeping secrets from one another about purchases, or being in denial about your spending habits. Own up. If you can't be honest about it, then you already know you shouldn't be spending the money or buying whatever it is. Even if it is a good thing, if you do not have the money for it, and can't tell your partner, then don't do it.