1. Hang out in window light.
The best light is natural light. So, if you're near a window, things are going to look 100 times better than if you're getting ready at the back of the hotel room next to a table lamp. Sat at the window facing outside is going to make it a tonne easier to put your makeup on, and make it so much easier for great photos, for the hair person, for the make-up person..
If you catch your photographer turning some lights off at prep, it's just because things look so, so much better in natural light - and natural light alone. When there are two sources of light; natural and artificial, things can look a bit meh. They will turn them back on, but if we can do without them, so much for the better. That of course depends somewhat on where you're getting ready.
Not to get technical - but this isn't an issue in rooms where there is no other source of light. Obviously in the hotel bathroom, that mirror light will look brilliant (and is all we've got), so leave lights on where you have to, turn them off where you can use window light instead. It's the mixture of natural and artificial light that is the problem. If there's no natural light, there's no problem with artificial light.
2. Be present in the portraits.
If there is one thing to take out of this list, it's this. When you take a stroll off, just the two of you - focus completely on one another. You don't need to meditate and find inner sanctum (unless that's your thing) - but just clear your mind of everything that isn't you two, and the beautiful commitment you have just made to one another. There can be a lot going on on the wedding day, a lot to think about, and perhaps even stuff to worry about depending on how you deal with social gatherings. Your photos will be so, somuch better if you just switch all that background noise off when you're alone with your bae. Plus that time will be so much more special - and unless you're eloping there can be precious little time when you're actually alone together.
3. Don't be bossed around on the day.
Registrars, vicars, planners, venue managers, suppliers all do a lot of weddings, and inevitably have their own views on the best way to do it. But there are very few things that have to be done a certain way. There is a declaration you both have to make, probably audibly to one another, and you have to sign there certificate in front of two witnesses. There is nothing else that you have to do. There is no specific side you each have to stand on, you don't have to face the front when one of you is walking in.