Just Say It.
You might be surprised how effectively you can write. It's the "getting it down on paper" that jams some people up. So don’t sit down to write. Instead, get a tape recorder. Find a private place. Maybe put on some music, but softly, so you don't obscure your voice on the tape. Then, just speak. Say what you really want to say. Be honest. Don't worry about the words. Take your time, talk more than you need to, if that will help. Then replay the tape. Find the phrases or sentences that really work, that communicate your true intent. If something on the tape makes you laugh, cry, smile, it’s a winner. Copy it all down, without worrying about grammar, completeness, or the order of the ideas. You might want to write each phrase on a separate index card. Then begin to determine an order for the cards. You can arrange and rearrange them until you get it just right. Fill in any gaps if needed. Then transcribe it all onto complete pages. Guess what? That’s writing.

Less is More. Be Simple.
Good writing doesn’t require big words or long sentences. It should aim to successfully communicate particular thoughts, sentiments or ideas. Pare things down to their basics. Keep it simple, direct and honest.

Be Specific.
Think about the writing that has affected you. If you are like most people, it is not generalized treatise on broad themes; rather, the most compelling writing is usually composed of small, specific messages or anecdotes that rang true. The great filmmaker David Lean, whose films include Lawrence of Arabia and Doctor Zhivago, once said that a great movie was really just a movie that managed to contain five great scenes. The five great scenes, if truly great, made the whole movie good. So it can be with your vows. Every word, every sentence need not move the earth. But try to come up with five moments that darn near do. The crowd will be mesmerized.

Stay away from broad generalities ("I will love you forever") and focus on small specific expressions of love. If you write about one specific event ("I promise to always dry if you wash, and wash if you dry") you write, by extension, about all events. If you try to write about all events, you usually end up not really writing about anything meaningful or concrete.

Pretentiousness = Bad Writing.
Pretentiousness is the hallmark of bad writing. Good writers explain and illustrate their ideas and their feelings, and do so in such a compelling way that you come to understand, perhaps to even agree with, the writer’s point of view. Bad writers make gross assumptions and rely on you to share their thoughts, feelings, experiences and opinions independent of what they write. Good writing communicates, enlightens and affects the reader or listener, and takes nothing for granted.

Avoid Cliches.
Cliches are a convenient crutch in writing. "My love for you is deeper than the ocean" will surely be understood by everyone but they’ve heard it a million times before. It’s unoriginal, uninspired. And your vows should reflect the profound inspiration of your love for one another. If it’s a phrase you've heard before, if it sounds like a line from a song, get rid of it. Find a new and original way to illustrate your point.

Have A Thesaurus Handy.
Remember the thesaurus? You leaned how to use it in elementary school, and perhaps you’ve never used one since. Well, you now have a very good reason to. The thesaurus, which gives you synonyms, is a great tool for writing. You don’t want to use the same couple of words over and over again in your vows. If "love" is contained in every line, people are going to get bored and ultimately the power and impact of the word will be diluted. The thesaurus is a quick and easy way to find alternate words.

Need some great adjectives to describe your betrothed? A quick glance in your thesaurus provides a slew: lovable, adorable; lovely, sweet; attractive, seductive, winning; charming, engaging, interesting, enchanting, captivating, fascinating, bewitching; amiable, like an angel. Use a thesaurus to find alternate ways to express key concepts. You might find it’s a great source of inspiration if you’re stuck and need some words to break you through.

Find a Friend Who Can Write To Give It A Read.
You may not know any "professional writers" but you probably know people who write as a part of their work. Not reports or factual analyses, but "creative" writing. Or you may know people who do a great deal of reading and thus have a good critical eye. Consider calling upon a friend (or make a new one!) who is a teacher, a librarian, who works in a bookstore, or is a member of the clergy. They may be able to give you some constructive advice on how to improve your writing.