The best way to make step-parenting work is for all of the parties involved to be on the same page. This may mean similar rules with each parent, or just an understanding of the differences in the rules. Make sure that the biological parents are both happy with the decisions, after all, you are talking about their kids.

As a step-parent the best thing you can do is not try to make the child feel like you are trying to replace their parent. You are not a replacement, just a substitute. Make sure that they understand that you are there because you love their mom or dad and that you want them to be happy and their mom or dad to be happy.

Be very careful about talking about your spouse's ex. Even if you don't think they are anywhere around, it can kill your relationship with them to hear to talking bad about their parent. Make sure that you are always saying good things about them to other people too. Find something that you sincerely like about them and share it with others, this will help them see that you don't hate them.

You are stepping into a very tricky role in their lives. You need to discipline, but you are likely to get a "your not my mom" response or "only my dad can tell me what to do". This can put you in a tough spot. Make sure that you develop a relationship before you start disciplining. Make sure that they know you are a part of their lives and that nothing they say is going to make you leave.

Talk to the kids, find out what role they want to you play in their lives. With older kids especially, they will tell you where there is a void. Maybe they need you to step into a parent role for whatever reason, maybe they want to be a friend they can talk to, or maybe they just want you to be their parent's spouse and that is good enough. But make sure you know how they feel about you and where they want you in their lives.

Develop trust with your step-kids. Let them know that you are there for them and that you are another support for them. They may take advantage of it and they may not, but put the offer out there. Maybe it will just take time for them to let you grow on them. They may hate you at first, but grow to love you when they see how you love them.

Don't put on a show, be yourself. And be yourself to their friends too. If you are being fake, then you will never find sincere love for them. Don't expect to be perfect at the role at first, grow into it. Start off with mistakes, like a normal parent does, and learn from them. Don't expect perfection out of yourself or your step-kids. Just expect from them what you expect from yourself.