Been to loads of weddings over the years. These are my suggestions (for what they're worth):
If you have two cousins of exactly the same age, don't invite one of them to be your bridesmaid and not the other. It is bad form.
If the wedding is not at the reception venue, then make sure there's no more than 15 or 20 minutes travelling between the two.
Ensure that there is loads of transport.
Don't leave guests hanging around for hours on end with nothing to do and nothing to eat or drink while you have endless photos taken. An hour and a half's wait while being plied with drink and canapes is plenty.
Sit like with like.
If there are younger guests present, make sure that the caterers serve the children's main course at the same time as the adults get their starter. There are few things worse than trying to entertain (and keep quiet) fidgety, bored and hungry children while you eat your starter and make small talk with people you've never met before and who look on your offspring with barely veiled annoyance.
And if you are spending hours having a million photos done, try and make sure that all relatives are included in family group photos and not just in the riff raff 'everyone all together' one at the end.
And... MOBs - don't be surprised if your husband's brother and his wife and children don't buy any photos of your offspring's wedding. Take a long hard look at all the umpteen official photos and you will notice that we weren't in any of them. We stood there like lemons among all the other relatives watching the photos being taken, and waiting for our turn. This family group. That family group. Aunts, uncles, cousins, grandparents, Uncle Tom Cobbley and all. It is embarrassing and insulting to find that you have been forgotten. And I know it was your doing, because none of your side got left out, did they?