Yes, that's the hard bit, and I'm no expert at that. I expect it would take more than an email. Getting to know people and forming solid relationships is probably the best way, but I'd be interested in what the experts advise. There is a lot of discussion about this online, but a lot of it is not necessarily reliable. The whole backlink issue gets pretty murky. (I just figure that if people like what I do, they'll link to it; so that's why I suspect it's ultimately better to focus more on relationships than links.)
Of course, one thing you can do is write articles and so on.