Ideally, you and your partner should have agreed the roles you're going to play and the rules you want to live by, before you move in together. Whether you're resident or non-resident parents, it's the birth parent who will hold the key position of authority and responsibility.
Take some time as a couple to consider the following:
How will you manage the relationships with your respective ex-partners? How will you manage your time so that everyone feels included? What rules do you want to have about mealtimes, bedtimes, tidiness, housework, homework, going out and so on? How will you organise the rooms in the family home? Who will be responsible for discipline and how will it be handled? How will you manage finances? What arrangements will you make for visiting stepchildren and other extended family? What will you do about special occasions such as birthdays?
The importance of clear communication Be honest and open with children when discussing areas that you know may cause difficulties. If it's particularly difficult with an ex-partner, or finances are strained, then acknowledge this in language appropriate for the child's age.
Children hate feeling they have to act like everything's OK when obviously it isn't.
Whatever rules you agree, it's absolutely essential that the two adults in the home are consistent. There may be different rules in the other parent's household and that's OK, but within yours there should be no doubt whatsoever where children stand.
Whatever type of family you live in, things change. As children grow up, rules often need to change and relationships with step-parents and siblings develop and shift. Some families find it helpful to hold regular family meetings to allow everyone to express their concerns, explore solutions and plan for the future.