Don't turn your date into a villain
Trite though it may sound, this final point really needs to be driven home. I've seen couples get into arguments over trivial matters that, in the long run, ended up making the least out of a perfectly good weekend.
If you've been preparing all year long to go on your big convention trip and you find yourself feeling less than enthused, step back, reset your perspective, and remember that this is all about fun. When you are there with someone you love, there is always a possibility for disagreement. That said, when you stop and consider what you are there for, it's all that much easier to have a fulfilling time. Share in each other's company and geekdom. Make the most out of your time because it will be over before you know it.
With anything new, there is always a learning curve, and attending a big convention together is no different. If you take the time to truly enjoy yourselves and each other's company, you are sure to have a lovely and memorable time together. Happy Con-ing!