#1 Strengths & Weaknesses. Before you do anything, sit down with your bride and talk about each other's strengths and weaknesses and how you can both help each other through this process. The ideas in this list are starting points, but you should really try and utilize what you're good at to help her out. For example, if you have a talent for calling people and making appointments, help her set a session with the florist, the photographer, the reception site, and more. If she has a knack for travel, let her plan the honeymoon.
#2 Emotional Support. Remind her that you're they're for her. Talk about both of your fears, anxieties and what you're excited for on the big day. If your bride knows you're supporting her through this stressful time it will relieve some of her tension and help you get to know her that much more. This is a great way to build communication before the wedding as well as learning how to work as a team as you help her plan the wedding.
#3 Registries. Help your bride with the registries. This is one job that will take longer than you or her think. Many wedding websites offer checklists of things you should consider as you visit the various stores that have registries. Set aside about two weekends in a row to check out registries. The first weekend visit some of the stores with no pressure to register for anything. It'll give you a good idea of what's out there. The next weekend get out the clicker gun and visit the store or stores you're interested in. If you're looking for gadgets and fun stuff, I'm a personal fan of Amazon.com's wedding registry (aff link).
#4 Wedding Website. Set up the wedding website. This is an easy and fun way to help. The Knot offers a great free and easy wedding website. Upload the time of the ceremony and reception, make a digital album, and connect your registries to the website. Write up bios for your groomsmen and get her to write them for the bridesmaids. Make sure it has a map to all the events and possible hotels your guests can stay at.
#5 Honeymoon. Plan out the honeymoon and wedding night hotel. Groupon.com (aff link) offers a wide variety of travel discounts under their "Getaways" tab. If you can manage it, try to not fly out to your honeymoon destination early the next morning. Take your time. Sleep in. Relax. Also, try and make your first married night really nice. Order something special like flowers, wine, or a candle for the room just to reminder her how much you love her.
#6 Invitations. If your bride is doing her own invitations, help her address all of them. Don't just throw her a list of names and expect her to figure them out. This process can be very draining, especially if she doesn't know many of the people you want to invite. Printing off return labels for the RSVPs is also very helpful that way you don't have to write them all out.
#7 Food. Talk about the food and what you would like. Believe it or not you can help her choose! Maybe she's already made up her mind but chances are she won't want to choose something your family won't want to eat. Sit down and talk about how much or little you think would be good. Are you thinking about having a buffet or various stations. Will the servers bring the food to the tables or will you get up to get your food. These are important aspects of the dinner to discuss.
#8 Finances. Create a wedding budget using an excel spreadsheet to keep track of expected and actual expenditures. Some websites actually offer wedding budget tools that can be very helpful. Making a budget involves you both clarifying who exactly is paying for the wedding and how much money you plan to spend. Do this one sooner rather than later so you can better plan for your purchases.
#9 Ceremony. Take an interest in the ceremony. Sit down with your bride and work through the ceremony, figuring out what you would and would not like in it. Do you want music, if so how much? Would you like scriptures on love or blessing or a passage that has meant a lot to the both of you? We have a basic Wedding Ceremony Outline that you may find helpful. Pay close attention the the vows! These are important words that will bind you two together for the rest of your life.
#10 Volunteers. Help get volunteers for the various activities. Make sure people are where they need to be. Do you need babysitters, greeters, ushers, people to pick up the flowers after the ceremony, someone to arrange the church stage, someone to put the drum set back afterwards, someone to move the sound system? Ask your bride what volunteers she thinks you guys will need, come up with a list of potential candidates, then take responsibility and go out and get them!
#11 Rehearsal Email. Know the date and time of your wedding rehearsal? Great! Type up the info so you and your bride can email it out to your wedding parties and anyone else who is involved with your ceremony. Make sure you have the after-dinner location picked out and call the restaurant if you need to reserve a bigger room for your party. Don't forget about inviting extended family if you want them to come as well.
#12 Tuxedos. This one may seem obvious but is one of the easter activities. You get to pick out the tuxedos or suits for you and your groomsmen! Arrange for you and your bride and maybe even the best man to go and choose them. Men's Warehouse and Al's Formal Wear are popular widespread choices for these sorts of rentals. Follow up with your groomsmen to make sure they get fitted for their tuxes sooner rather than later. Also, arrange for your best man or one of the groomsmen to take care of your tux after the wedding.
Want to be even more helpful? Get your bride The Wedding Book (aff link) and look through it together to figure out more ways you can help.