When you are doing a beta launch and trying to drive downloads, you have to focus on three areas: identify your early adopters, identify the right messaging to get them to download, and make sure the landing page is enticing. You have to focus in on narrowing down the initial groups through testing via facebook ads and seeing response rates. Alot of lean startup here, build measure learn. Figure out what works and why. Know what drives your customer to want to use your product and market towards that side. Example is if your email productivity app, look at peoples who interest on facebook is inbox zero... Be specific enough to learn.
I know this isn't techniques, but with a beta release you have to market towards people who are willing to take a leap of faith with your product, go into the unknown and more than anything they want to go and try this out!