what would be the best approach for copy on a pre launch page, where the end goal is to get people on an early bird list, people on this list will get guaranteed discounts, and extra features of a wordpress plugin.
I would study lots of the current pages out there - just Google apps, plugins, gadgets, software, etc. coming in 2015 and see what you can find.
They generally go for either the long page panel approach (panels that fit your browser window > next panel scrolls up > parallax effects, etc.) or the single page. The ad copy is usually quite short with images/graphics and bullet points of sorts.
When it comes to ad copy, as always you should highlight the benefits of whatever you're selling asap. Do you have mockup/examples you can show to tantalise them?
Whatever the case, or the product, you can split test plenty of landers to optimise for those opt-in rates.