If you want to make it to the top, start at the bottom, say the experts. Internships can be the fastest way to get your foot in the door at a dream company and start scaling the ranks. A 2012 survey by Internships.com showed that among companies with 100 or more employees, nearly 70 percent made full-time job offers to their interns. These all-star interns turned positions at the bottom of the company totem pole into enviable executive gigs. Here’s what you can learn from their experiences.