Having done more weddings recently here is my top ten list of dos and don'ts:
Don't ask the registrar if you can do the interview after the ceremony. It's a legal requirement and a hard no.
Do think about the location of your wedding and your outfit. It's a shame to see beautiful heels and dresses covered in mud and dirt if you've had to walk outside at all.
Do practice sitting in your dress. It's likely you will need to sit to sign your marriage certificate. On this note, please make sure you wear underwear if it's on the short side. I have seen a surprising amount of unexpected undercarriage.
Don't ask the registrar to hold your miniature tea cup dog in a bag for the duration of the ceremony. Also a hard no.
Don't flirt with your registrar.
Don't be drunk or allude to drinking lots prior to the ceremony. It will make your registrar be suspicious.
Don't be late. Registrars want to start on time as we have other weddings to get to.
Don't make jokes about still be married to your ex. We will take that seriously. Yes, Las Vegas weddings do count.
Don't have religious content in your (non religious) ceremony. Yes this includes hymns, vows and speeches (which we will want to approve in advance). Don't think we don't know how to use google translate.
If you are a lawyer, refrain from telling the registrar that 'you know the law'.