If you want to be published well, you have to start off by doing plenty of research.
Do your research before you start writing, so you know if your book has commercial potential and if you really know what you think you know, or if it's actually all assumption and myth.
Do your research before you start editing, so you can distinguish between things like ellipses, dashes and hyphens, and know when and how to use them: otherwise your work will be sloppy and unpolished, and it won't impress anyone.
Do your research before you start submitting, so you only send out to reputable agents and editors and avoid the ill-intentioned and ill-informed who will mislead you, and cost you time, money and tears. Remember that nice isn't the same as good, and that in publishing, experience counts.
Do more research before you start submitting so you only submit to agents and editors who work in your genre and are accepting submissions.
Do your research before you agree to anything, to make sure you're not restricting yourself uneccessarily: I particularly dislike unlimited exclusives.
Do your research before you sign anything, so you don't end up committed to an inappropriate agent, or tied to a poor publishing contract.
Do your research before you take anyone's word for anything, especially on the internet, where new self-appointed experts (like me!) pop up every ten minutes.
And finally, although it's wise to be cautious and research is invaluable, not everything is black and white and just like writing, publishing isn't a one-size-fits-all, yes-or-no endeavour. There will always be exceptions to every rule: just make sure that you learn to separate the new-and-exciting from the old-and-scammy, and the creative-risk-taking from the foolhardy-and-dangerous.