How to become a runner
The best way to get into the industry is to become a runner, however getting your foot in the door can be difficult because there is so much competition, and the difficult thing is that if there is one person who is slightly more experienced than you, you become second best.
The most important thing to remember when trying to get into the industry is to remember that no job is too small or insignificant. Do not say no to a job just because they may be doing work that may not interest you, or that is not broadcast or film work. Just because you may be doing small corporate videos for online does not make your experiences any less valuable.
Work for free! Even if you just work on the weekends or after hours, everything on your CV and on your showreel counts. It would be better and more fun if it is your own films, but being able to show that you have worked for companies, and be able to follow instructions is also good. In this industry it is more who you know than what you know, so having a well known company on your CV (even if you worked there for free) is worth it.
You must be willing to make loads of cups of tea and get lunches and do fetching and carrying. In post Production houses, being a runner is mainly making tea. Even if you want to get involved in Post Production, I do not recommend working in a Post Production House. You get way more experience working in a Production House than in a Post Production house.
Smaller companies are the best places to start. Smaller companies have less money to hire more staff, so being a runner at a smaller company, you will be able to help out on loads of other more interesting small jobs that will give you experience in different parts of Production like researching or even some editing or post production work.