There is no way to increase your odds per say. As long as you are doing your daily emissary, you're doing it right. You could spam heroics. Some people have gotten lucky there but there are no promises. I know people who have done upwards of 300 to 500 heroics and still have not got a legendary.
Out of all of the people in my guild actively playing (40 or so people), only four legendaries have been acquired. Funny thing is, out of the four legendaries we have, two of them belong to a single unholy DK in our guild (one from a heroic, the other from an emissary). And yes, the entire guild hates him and he was kicked for a brief period so that we all could feel better.