I know I am running behind in responding but let me put in my four or five cents here. As a step mom for the last two years to a boy and a girl I have some insight....
1. Never talk bad about the other parent. No matter how stupid, ignorant or assinine the bio parent is...you will almost always be second and until they learn better, talking bad will only make you look bad to them. (granted it took me a while to learn this one!!)
2. Do not dicipline in any way that you would not your own biological children. I do not recommend spanking step kids. It will just get you in the spot where you are the bad guy.
3. Do not try to be the kid's "friend" You are a parent. Granted you want to have fun, and you want them to have fun. But being a parent first is always important.
4. Do not buy their love. I thought by buying them darn near anything they wanted. Darn was that a hard one to learn!
5. Respect them as much as you expect them to respect you.
6. If they refuse to respect you, do not accept it as a personal affront to you, they are still children. Make sure that your spouse backs up YOU first, the kids second (unless your doing something obviously wrong)
7. Take time for you and your spouse. Being a step parent is hard, I am a full time step parent as their mom is only in the picture for visitation one day a week and it is hard when I went from not having kids around to having them around 24/7, it was quite a transition and I learned that a good $30 babysitter and a night out with my husband is invaluable.
8. Take time for just yourself. your husband works and leaves you to care for the kids but you too deserve an out. Make sure your keeping in touch with your friends and family and enjoying the alone part of life too!.
Good luck. it's not easy but it get's easier as it goes along