Here's some real advice from a recent Newlywed.
If I Could Do It Again, I Would:
I would double, triple, and quadruple check my contracts, even during the last week leading up to my wedding. I knew basically what I was entitled to with each vendor, but knew no specifics and forgot to bring the contracts with me. When my limo arrived, the driver would not let me in until full payment was recieved. I had arranged for my Future Father-In-Law to handle payments and tipping and he wasn't due to arrive for another hour at a different location. The driver refused to let me in until one of my bridesmaids finally volunteered to give him a check. It was a stressful and terrible experience. Make sure that you read your contracts, bring them with you so that you have backup, and talk to your vendors in advance to confirm the timing of the payments and make sure that things run smoothly!