I feel like in recent years, the groom's role has diminished in the wedding planning process. The groom is supposed to choose the engagement ring but many women show pictures and drop hints about their dream ring. The groom is to choose his wedding party, but if your bride doesn't like one or more of your friends, good luck getting them in. And you're supposed to choose the groom and groomsmen's attire. It is your day too! One day you'll be telling your kids or grandkids about the day you married your wife. Make sure that it has your stamp on it.
Express yourself. The theory that men don't care about their wedding day really isn't true. You probably haven't daydreamed and practiced in the mirror like your fiancée has (she has whether she admits it or not) but you've thought about it a little bit. If there is anything that you feel strongly about that you want, speak up! I once knew a groom who insisted on having an ice sculpture at his wedding. He didn't care about anything else at the wedding. It's fine if you have one aspect or ten that you really care about. As you meet with the vendors, if you have a preference, stand up for it.
Participate please. Meet the caterer. Interview DJs. Be a part of the planning. The reason many brides take over the planning is because they can! A lot of grooms only participate in conversations involving budget. It's not always realistic to expect the groom to invest as much time as the bride does but that doesn't mean you don't have to invest any. The more involved you are, the easier it will be for your love to appreciate your input.
Be the level-headed one. Some women, not all, become more emotional than usual. They're stressed and busy and not everyone cooperates. The time will come when her mother, best friend, or your mother gets on her nerves. This is the time for you to step in and diffuse the situation. Listen when necessary, referee, and empathize. Don't escalate things. Your goal is to have all relationships intact once the wedding is over.
Keep your guys in line. Take charge of the communication with the groomsmen, ushers, and ring bearer. Make sure that all of their travel arrangements are in order and suits purchased/rented. Remind them of important dates and if you need to have any uncomfortable behavior questions with some of them (perhaps some of your rowdy frat brothers) do it and leave the bride out of it.
Arrange some surprises.. I like the idea of a groom taking charge of a few details of the wedding. If you do everything else on this list even the most neurotic bride won't have a problem relinquishing some details to you. Take on the honeymoon (which FYI, is a groom responsibility) and don't tell her more than she needs to know. Buy her a wonderful wedding gift. Something that lets her know that you're looking forward to your future as much as she is. Throughout the engagement, do romantic things that remind her of why she's so jazzed to marry you.
It occurs to me that many brides have a hard time letting go because we don't always feel that the day means as much to you as it does it us. If you can make her feel that your wedding day is important to you as well you'll have a much happier bride and a better wedding planning experience.