One way to write good anniversary messages is to focus on a message that is unique and that adequately reflects your relationship with your significant other. One example is telling your significant other that once a year is not enough to express how much she continues to mean to you.
To create a more customized anniversary message, begin by writing a sweet sentiment regarding how it feels to be together. Next, write how you feel about this person, and then write out a compliment about this person. End the customized message by expressing your gratitude for the presence of this significant other. As the message should reflect the personality of the person writing it, it is acceptable if a person who typically worries about saying something wrong keeps his anniversary message short.
Some example messages mix in common expressions with sweet sentiments for your significant other. An example is to tell her that it seems like time is flying due to it being another year together already, but that time seems to be going faster because you are having so much fun with her.
An example of a sentiment meant to encompass the full range of experience and emotion you share is to wish a happy anniversary to someone with whom you can speak, sob, chuckle and cause much trouble.