Same-sex weddings are very similar to mixed-sex weddings, only the legal certificate may not be there. As the UK doesn't yet recognize gay marriages, the recognition and celebration of your union is often referred to as a commitment ceremony, but the function is the same--to declare your love and devotion to one another in the eyes of your friends, family and sometimes, your church. It gives your commitment a feeling of permanence, and of course, gives you a reason to throw a fancy party afterwards! In many ways, you may have more flexibility in your ceremony and reception than a heterosexual couple, especially when it comes to vows, readings and formal processionals, so have fun with it.
There are a lot of different options when it comes to the officiant. You can still ask a judge or justice of peace to sanction your wedding even though the ceremony will not be recognized in the legal sense of things; they will be doing so symbolically--nothing legally binds the two of you together. You may also be married by a priest, minister or rabbi as long as they agree to do so. If you are in a more relaxed or reform religious setting or you've known your officiant for years, chances are the individual would be delighted to help you take this next important step in life. If you're looking for a more "non-traditional" officiant, why not have a close friend or relative perform the ceremony? And if you fear you might offend someone by not picking them to participate, try contacting an Ethical Humanist officiant (these individuals are part of a religious movement dedicated to social justice).
Since you may not have set legal or religious proceedings to go by, this is a great opportunity to craft your dream wedding ceremony. Sit down with your spouse-to-be to decide what should be said as the ceremony begins and you are both recognized, along with your vows and the readings performed during your ring exchange. You have freedom to adapt any and all readings from poems, songs, excerpts of novels and whatever else may have an important meaning to the both of you. For some specific ideas on how to go about writing and/or choosing your vows, check out our wedding vows guide.
This is the same for same-sex couples as is for mixed-sex couples; technically, you can wear whatever you want! There are traditions--formal wear is usually accepted over casual wear and white is always in style.
The rest mostly depends on personal preference. If you're getting married in a religious building, think about how you will walk down the aisle. Perhaps you can walk down separate aisles before the ceremony, and then walk together down a single centre aisle once the service is completed. Make sure you assess the space and its ability to accommodate your wishes before you book it!