The vows that a couple takes as they wed should represent their specific expectations and desires about their marriage. A guided discussion can help them focus on what they each feel is important, and identify which of those elements should be proclaimed aloud at the ceremony. Vows can be the same for both members of the couple, or each person can promise different things to the other.
Wedding vows are promises, whether they are associated with a specific religion or not. As promises, they should only include things that can be controlled by the people doing the promising. The actions can be general or specific, depending upon the desires of the couple, and can fall into a number of categories:
Areas that are hard to control include emotions, number and gender of children, and specific levels of income provided by each spouse. It's perfectly acceptable for a woman to proclaim her love for the man she is about to make her husband, but it's not wise to promise that her love will last forever. A better choice would be to promise loyalty or fidelity.
Once a couple agrees upon the content of the wedding vows, the artistry must begin. A laundry list of tasks and obligations will bore the audience and be meaningless to the participants. Couples who choose to hire a third party to write their vows are depending upon that writer to make their promises eloquent.
How the vows are to be spoken is an important consideration. In many ceremonies it is common for the wedding celebrant to ask the participants to repeat the vows, line by line, after they are read aloud by the officiant. Other couples may choose to memorize the entire list of promises. Also acceptable is for the couple to read prepared vows directly. How the vows are delivered factors into what they should contain: memorized vows may need to be shorter, for example, and read vows should be written with an eye to avoid hard-to-pronounce words.
For more information on writing vows, visit The Knot's guide to writing wedding vows for couples.