The importance of publishing credits is a largely-debated aspect of the journey from “planning a piece of work” to “accepted and published”.
I spent my spare time at university volunteering in the area I wanted to find work in. I found part-time work to bring in money, and part-time volunteering to get enough work experience that would give me a) skills and b) something to stand out from other people applying.
The same is true of wanting to get your work published.
Currently I have credits for poetry, but when querying publishers/agents for a novel, it’s probably more useful to have some short story credits as well/instead.
This is the stage I’m at – submitting some small pieces of fiction to a variety of competitions and publications. I have flash fiction competitions, monthly prompt slots for specific magazines and short stories being planned out. I’m applying to things I wouldn’t want to win the prize of anyway, or finishing a piece ten minutes before the deadline and submitting it anyway. Because one day, my entry might still be one of the best that time around.