Before the 1950s, what was the principle tactic used by members of the civil rights movement to press their cause

They mostly took legal action. At first, after emancipation, former slaves expected full voting rights and forty acres and a mule. The law failed to provide them this, but they still campaigned for it. They brought many legal cases up in court to accomplish aims like abolishing the one drop law and restoring voting rights, but most were ineffective.