God knows what you can and cannot give; He also knows how much you must have to meet your family's needs during the coming year. When the Christians in Antioch heard that some of their fellow believers were in great need, they gave "each according to his ability" (Acts 11:29).
At the same time, most of us could be far more generous to God's work than we actually are. If you give your church only what's left over at the end of the month, you'll probably not give very much, for money has a way of getting away from us. Do you have a budget, and is everything in it really necessary?
Many people find it helpful to set aside a certain portion of their money for God's work on a regular basis usually when they are first paid. Paul told the Christians in Corinth, "On the first day of every week, each one of you should set aside a sum of money in keeping with his income" for God's work (1 Corinthians 16:2). Even if it seems like a small amount, I strongly encourage you to give regularly to God's work.
The real issue, however, is this: What place does Christ have in your lives? Is He only one of many interests or is He the center of your lives and your family? Make sure of your commitment to Christ and then ask Him to help you use your money for His glory and not just for yourselves.