Species traits have much to offer conservation science. However, the selection and application of trait data in conservation requires rigor to avoid perverse or unexpected outcomes. To guide trait use, we review how traits are applied along the conservation continuum: the progression of conservation actions from assessing risk, to designing and prioritizing actions, to implementation and evaluation. We then provide a framework for their use as proxies for more nuanced empirical data on species and ecosystems. Framework steps include (1) identifying information needs relative to conservation goals, (2) choosing relevant traits using theory and expanding via expert elicitation, and (3) defining and addressing the limits of trait information. Worked examples for contemporary plant and amphibian conservation show how traits should be selected and applied based on theory and/or evidence (rather than data availability or untested assumptions). Finally, we forecast the use of trait data in several conservation applications globally.