Sooner or later, for the majority of us kids will enter the picture. Hopefully they will come about as the result of a planned and happy marriage, but sometimes that just isn't the case. Sometimes, even in our modern world, marriage is the result of an unplanned pregnancy and sometimes pregnancy comes when least desired or expected. In any event sooner or later most all of us become parents and as any parent can attest kids can cause a whole lot of stress.
First and foremost remember how special children are. But more than that bear in mind how important each individual in this world is and more especially the great opportunity you have as a parent to help that individual become something truly special. One of the most important things any parent can give a child is a stable and loving home where they feel the nurture and support that they need.
Talk with your spouse about the children both before they come and often after they arrive. What are your expectations? What do you want to be able to give your children? What kinds of rules do you want? What kinds of activities do you feel are important? Be prepared to be surprised by your spouses responses. They very likely have very different ideas and that is a very good thing. There is no one correct way to raise children, there are a lot of different right ways (and quite a few different wrong ways as well). By incorporating ideas from both partners you will be alleviating the one sure thing to harm your children - stress in your own marriage.
No matter what other successes they may experience, your children will remember the way that you feel about your spouse above all else. When they become adults and enter into their own relationships they will carry those feelings with them. You can expec that they will make the same mistakes that you are making today.
So plan activities that involve the whole family where possible. These need not be expensive vacations to them parks or resorts. A day in the park will do wonders for their attitudes, as will a round of Monopoly or a hand of cards. If your family is not accustomed to spending time together this may grate at first and even feel forced, but give it time and the good memories will develop.