1) Discuss future plans including
A) finances: know what each of you OWES, discuss budgets,
and spending/saving habits. You cannot effectively plan or
*have* anything plan if your finances are out of control.
B) children: if, how many, and when along with child rearing
philosophy. If one of you stringently wants 3 kids *right
now* and the other none, this can lead to major conflict.
Also, if one believes firmly in spanking and the other does
not (just an example), conflict can arise.
C) educational and occupational plans: when, where, and how
to finance. What a shock to realize that the other plans on
moving you away from your family.
2) Family: do not just "meet" the family. Get to know the other's family. When you marry someone, you also marry their family. Know important family traditions and if that persons wants to be near his/her family. Sometimes knowing the family secrets and rifts helps to make the transition easier.
3) Discuss and decide on religious views. When two people come from very different religious backgrounds, it is easy enough to say, "I will go my way and you go yours." For some this works, but after 5 years or so of marriage and no agreeing, it can get lonely attending services alone. This also has implications for the children.
4) Discuss and plan a way to manage fights and disagreements. Lay down ground rules.
Just my 2 cents.

Silver
Edited for my horrible grammar....