There are two little things that a writer can do to make sure they don’t get trapped in the slush-pile.
First, make sure their work is ready to submit before they send it off. The vast majority of submissions (perhaps 95%) are nowhere near good enough to be published. I’m not talking about work with a few typos, or in need of restructuring: I’m talking about work which has absolutely no chance at all of ever making it into print in the commercial market.
Second, make sure they target markets which are appropriate for their work. You wouldn’t, for example, write an article about breastfeeding and send it to a car magazine: so why do so many writers do the equivalent when submitting their books?
The company I edited for specialised in illustrated, esoteric adult non-fiction. It published books about meditation, religion, prediction, mythology, retreat, and tantric sex. Submissions included novels, pornography, and proposals for books about cars, weaponry, and computing. The most fantastic submission was a heavily-illustrated children’s story book, in verse, about trolls. All written in Dutch, with no translation provided.
No wonder so many of the bigger publishers will now only accept agented submissions, and reject other submissions unread. No wonder so many agents are now closing their doors to new clients.
I’m not telling anyone not to submit. Just make sure that you’re ready, and that you’re sending your work to the right place. That’s all.