Convince those whose choices are currently hurting animals to make more compassionate choices.
Everyone can alter their choices in ways that will help animals. The key to getting people to do so is to make it easier for them to do so.
That is: the less people have to change, the more people will change.
Regardless of the personal opinion of any particular current vegan, giving current meat eaters what they want -- familiar, tasty, convenient -- is the way to help animals. This article by The Telegraph is one of the best discussions yet of how this could play out. Excerpt:
But [Brown's] approach is clear: to take plant tissue and re-engineer it to look, smell and taste like real meat. He has, he says, “no interest in making products for vegans”.