Your wedding vows are the most important part of your wedding day. If nothing else matters, your vows should. They are what will bind you in matrimony and represent your commitment to each other. Work closely with your officiant to decide if you want to have traditional, religious, or personal vows.
For traditional or religious vows here's a guide to help get you started: https://www.thespruce.com/sample-wedding-vows-3489433
If you're writing personal vows here's some guidelines on the what's, the how's and the where's:
Your vows should reflect upon your relationship and lay out the promises you wish to uphold in your relationship. Some people choose to go all serious while others insert humor into their vows. My brother vowed to always let his wife bring snacks to bed. Funny, but also a serious promise as she is a serious snacker.
Vows should only last about a minute. Pick the most important promises and get at the heart of what marrying this person means to you. I promise that one minute lasts longer than you think. You also don't want them to drag on because that extends your ceremony time.
WRITE THEM DOWN. WRITE THEM DOWN. WRITE THEM DOWN!! The last thing you want to do is get up there and go blank. Write them down!! Here's an alternative to a wrinkled piece of paper (there are tons of different types, you can even get them personalized)
If you're like me and you're terrified of speaking personal words in public (I'm a crier. Big time.) but you still want personal vows, you can choose to recite your vows in a semi private setting (just your photographer and planner) during your first look/touch. This gives you the opportunity to recite vows, get it documented and get the tears out. That being said, it will not guarantee that you won't cry during your repeated vows at the alter.
PRACTICE. Recite them in front of the mirror and in front of a trusted friend. Get all the jitters out and practice, practice practice.
Remember, your vows are personal and however you choose to do them, they will mean the world. Work closely with your officiant - there are some phrases in some states that are required by law to be said for a marriage to be official. Also, have fun with it. It will be a memory that will last a lifetime!!
If all else fails, and it fits in the budget, don't be afraid to hire someone to help you craft your vows: https://www.vowsandspeeches.com