1. Keep it private. The last thing you want is to give your child a reason to play you off each other, or to manipulate the situation. As far as your child is concerned you agree with one another, but have yet to make a decision. Then, discuss the issue on your own, out of earshot, and away from others. Whether the discussion is about curfews or whether or not your daughter can wear that revealing dress to the prom, it does not matter. Keep it private.
2. Determine if it is a principle or preference for you. Let's say you and your spouse are arguing over what you let your child out of the house wearing that morning. Your spouse was at work, and did not see what they were wearing, and you did not mind it. When your spouse gets home they are appalled that their child went out into public looking like "a tramp". So, an argument ensues. For your spouse it is likely a matter of principle. Modesty may be one of the values that are important to them, and they do not want to see your child so immodest. For you, it is not a big deal because you feel like kids should be allowed to express themselves however they want, and that dressing is a personal choice. For your spouse it is a matter of principle as it affects their core values. For you, it is preference. You prefer to let your child make those decisions on their own. In this case, your spouse should win the argument because it is a matter of principle.
3. Find a way to either meet in the middle, or choose one side or the other. When it comes to arguing about your kids you can't just agree to disagree. You won't be effective parents if you do not agree with how to raise your children. So, either compromise, or choose one side or the other. Even if you do not love the decision, you need to stick by it so that your child knows that whether they go to mom or dad the answer is going to be the same. In the above example, a compromise could be that when at home the child can dress how they wish, but for school, they have to follow a certain level of modesty.

The parent-spouse relationship can be a complicated one as you are taking on two different roles, and you are two separate people with separate ideas that have to be unified. However, your best option is to discuss the potential issues before they arise and make a decision before you ever even have children. You may decide that your kids can't date until a certain age, or that you will not be buying them a car when they turn 16, or that they have to have good grades to be allowed an after-school job.