Note: I have been involved with EA since 2-3 months only, so my ideas may not be accurate.
One approach is to target people involved in social issues who believe in some of the more popular EA concept(s).
Out of all the EA priority areas, climate change is arguably the most popular one (among non-EAs/general population).
Quite a few people (among non-EAs) work on climate change because they think it's the most pressing problem. They believe in some of the more well-known EA concepts like:
1. Using supply/demand concept to choose a social issue (aka neglectedness).
2. The fact that climate change needs to be fixed quickly while other social issues can be solved later also (similar to idea of existential risk).
On the whole, more involved groups appear to prioritise Global Poverty and Climate Change less and longtermist causes more. ~ EA 2019 Survey
However, I must point out that Global Poverty is ranked the most popular EA cause area, followed by Climate Change. I suspect this is due to a lot of people in the EA movement having joined recently, and taking some time to understand EA's ideas on cause prioritization.
Similarly, it may be efficient to target people who are involved in nuclear security (they share ideas of existential risk and sudden catastrophes are more important than catastrophes that build up over time).
Essentially, we are looking for people who are working on a particular social cause because of logical reasons. This greatly increases their chance of being a fit with the ideas of EA, since this approach captures both the effective and altruism aspects of EA.