It's been said that parenting is the toughest job in the world. Wrong. It's the second toughest: Stepparenting wins hands down. Right now, approximately half of all Americans live in a stepfamily, which means that every day, millions of women are subject to the taunt—sometimes mournful, often angry—“You're not my mother!""

I've been a stepmother three times. I know, from hard-won experience, that a great relationship with your stepkids is possible. And if you avoid certain trapdoors like the 4 verboten phrases here, you'll not only get along, but you'll never have to ask them to pick up their socks.
1. ""Go ahead, call me Mom!""
You're not their mother, and you never will be. They're conflicted enough, and pushing them to use a mom-name will only confuse them more.
You might eventually become the happiest of stepfamilies, but it won't happen overnight. Studies show the new family dynamic takes at least three years to fall into place, and the first year is the toughest.
2. ""Feel free! Do whatever you want.""
Almost as much as they need love, children need boundaries, and are adrift without rules. Learn to say (not scream, please) the following phrase: ""In this house, we..."" so that time together will not be bogged down with endless negotiations.
No matter how close in age you are to your stepchildren, you're still a parent figure; try to be an example of mature living and not 'one of the gang.' This is especially true if your stepkids belong to that group of psychotics euphemistically known as teenagers. Chances are they won't think you're cool for very long.
3. ""I'll get it,"" ""I'll drive,"" ""I'll wash it,"" ""Forget about me,"" etc.
Don't let your stepkids (or their father) turn you into the creature everyone in the world resents: a martyr. Martyrs make people feel creepy and guilty, and when kids feel that way, they generally act out. You're better off being wicked.
4. ""Why the long face?""
Your stepchildren are allowed to be sad—they're in mourning. Let them grieve if and when they feel like it. Sorry, but they probably will grieve more around you, since you're the evidence that their parents are never getting back together. Don't call attention to their sorrow; remove yourself, and get Dad to be a mom at this point. Their depression will pass—they're kids.
(Source: Oprah.com)