Achieve an initial stage; succeed with a first step. For example, I think I could do well in an interview once I get my foot in the door with an appointment. This term alludes to the door-to-door salesperson or canvasser who blocks the door with one foot so it cannot be closed.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.