Journeys triggering for new hires

I'm creating new tasks in Journeys for new employees and am new to the system. Aside from selecting the correct eligibility, how do I make sure something goes to the employee before their start date for pre-boarding? What do I need to select or set up to make sure a Journey tasks a) triggers to go to the new employee and b) triggers to go to the new employee before they start? Thanks in advance, stepping into this module with very few resources to reference.