Relationships with blended families offer a unique opportunity to take inventory of how much you and your children have healed the "family" you previously had. Nothing brings up the old resentments, fears and hurt from the divorce days more quickly than telling your children that you are moving in with a new partner...and all of the children. How well it goes can be considered a litmus test for your level of comfort with how you will not repeat the past.
The most important thing to remember about relationships with blended families is that you should take the phrase "blended family" quite literally. You may love your new partner to the end of time, but you have to hold the space that they represent half of a "family"...a family that existed before they ever met you. The man or woman you are about to move in with is showing up with their children from that family. In the hearts and minds of those children especially, you are the second marriage. You will always be the third parent, if you are ever considered a "parent" at all by his/her children. Looking into your new home from their eyes must be the highest priority. What you need them to see, for harmony to happen, is that you are supportive of where they came from. They must know that you understand what they went through. Hiding the uncomfortableness of divorce isn't going to help them. Trying to make them forget that they are not in a second "family" isn't going to help them transition.
What children in blended families need to know is that things are going to be safe and that there is room in the new home for who they have been and what they have been through. Time and time again many relationships with blended families end rather quickly. This is because they try to move on pretending that their joint pasts are just in the past. That is too much history to cover up with fresh paint and new furniture and a neighborhood with sidewalks close to the children's elementary school.
The past requires inclusion in the blended family. Things must be obvious and out in the open. Many therapists and professionals may say that speaking plainly about the past is too difficult for children. Consider this though...they lived through it already, right alongside the parents. Not talking about it, is not what they need. They need freedom to spend time talking about it.
You literally must blend the relational history of each side of a blended family if you want to ever experience life again as a whole family. You must bring into the center of the room whatever the children and new partner have brought with them and be honest about it. Blend what your "family" has been through before as well. Set it all out along with the suitcases and moving boxes. Don't leave it behind as if the past doesn't matter. For if you do, you may quickly find your new family, becomes another family that you almost had.
Blended families are hard work. Work at them hard enough though, and you will eventually be able to drop "blended" and just call it "family".