Marriage, one of the most important events in a person's life, can not be properly celebrated only once a year. It should be cherished daily and celebrated as often as possible. I try to informally celebrate our wedding anniversary on the 27th of each month (my wife and I were married on May 27th).

I don't always plan something elaborate. In fact, sometimes I only buy or make a card for her. It is nearly always a surprise what I plan so she doesn't know if she will receive a card or actually be taken out for a date.

If there is a movie or concert she has wanted to go to, I buy tickets for that. Or I take her to see a garden or museum on the weekend when we have more time to enjoy it. You don't have to be locked in on celebrating your wedding (or engagement or other special day) a certain day each month. Just try to celebrate it often and with creativity.
Ways to celebrate a monthly anniversary
◊ Buy or make a card
◊ Visit the zoo or museum
◊ Plan a picnic
◊ Go for a drive through the countryside
◊ See a concert or play
◊ Go out for a special (not necessarily expensive) dinner
◊ Order dinner in and drink champagne
◊ Go to the drive-in