How to win as a third party in American Politics

Suppose that there is a third party you support and would like to see become a viable contender in American politics. What strategy should you advise the party to follow.

Valence is key. The two major parties are able to beat your party because in a first-past-the-post system voters have incentives to vote for parties that can win. And because unknown parties do not appear credible to the voters. To win, you have to persuade voters that you are better than the other parties. That you have higher 'valence'. In particular this might mean that you are more competent at administering the government, that you are more honest, or that you are more charismatic. Unless you have a substantial valence advantage, the other parties can always prevent you from winning.