Bernstein points out that relatively successful third-party candidates tend to have "one or more of the following: fame, money, political qualifications and a built-in constituency":
The truth is that the way it really works most of the time is someone with a big ego and the resources to make it happen decides to run and probably then fills in whichever issues seem to resonate. Starting with the issues is pretty much getting the whole thing backward. If you want to push some set of issues, try to get a major party candidate to adopt them. It’s a lot easier.