My husband and I participated in premarital counceling, and our pastor kept telling us that it was almost a waste of our time because we had already discussed all of the topics covered in the counselling. However, (and that's a big however), he pointed out that most people often don't think to talk about some of the big things ahead of time. If nothing else it gives you specific topics to make sure you've thought through how your life will change when your two families become one.
Even though we weren't meant to have answers for all of these things, it was so we would talk about them (and we didn't have to discuss it in front of the pastor). Some examples of things we covered are:
Kids - how many, how far apart
Parenting - styles, responsibilities, discipline
Housework - who does what and how often
Holidays - how to celebrate, how to alternate families if you can't attend all holidays with both families
Financial stuff - how to plan a budget and stick to it, how to understand your spouse's spending style and work out compromises
Sex - what each expects, understanding sex lives change, and how to deal with temptation outside the marriage
If your goal is protecting your marriage, communication is the key. If you can calmly discuss issues, that will go a long way. Just food for thought - I saw a statistic during our premarital counseling that stated 1 in 1250 marriages where both spouses read the Bible every day end in divorce. Interesting. . .