The first step you need to take is to draw up a budget, and then stick to it. Not only does this help you to work out how much disposable income you have available, it also helps you to track where and on what your money is spent. This makes you aware of unnecessary spending and will assist you to eliminate some or most of it.
With all the demands of running a family, it's hard to find time to make a household budget -- especially if the amount of money left at the end of the month is less than you want. It's important to look household finances squarely in the eye, because that's the only way to control them; otherwise, they control you.