1. DON’T REFER TO THE WEDDING AS A PARTY
It’s certainly not a party, a commitment ceremony or a celebration, it is a wedding. And while I’m on that, don’t refer to any wedding as a party; be it straight or LGBT+. It can give people the impression that you don’t take their wedding and/or relationship as seriously as you might take others.
The couple have no doubt invested a lot of effort, time and resources into their big day. Be considerate not to spoil it for them by calling it anything other than what it is.
2. STOP AND THINK BEFORE USING GENDERED TERMS
You may or may not know the correct terminologies to use about or at a LGBT+ wedding; ignorance, unfamiliarity and simply feeling uncomfortable can all mean that you don’t know how to word things in general conversation.
But you can’t just choose to blurt out traditional, gendered terminology that is not specific to the couple. It can show that you didn’t care enough about them to learn which pronouns and language are appropriate for them.
3. LEARN THE RIGHT TERMINOLOGY
Every couple, be it LGBT+ or straight, have their preferences.
Being acquainted primarily with straight couples in the past means that the terminology and language to refer to them comes naturally to you. However, you should research about the different non-gendered orientations before attending an LGBT+ wedding. This shows that you respect the couple.
Listening carefully to the couple and sticking to the same terminology is a good idea.
For reference, it is generally easiest to use the couples’ first names or refer to them as a couple, lovers, you/these/those two or this pair.
But if you have a good relationship with them (which I’d hope you have if you were invited to their wedding) and you don’t know, ASK them which pronouns they prefer (she/her, he/him, they/them).