I read a lot of blogs on publishing. Sometimes a ridiculous amount. It started a few years back stumbling onto Miss Snark, and continues with Nathan Bransford, Pub Rants, Editorial Ass, Editorial Anonymous and many more. Read them. Go back to the beginnings and spend a day reading through the archives. They and those like them, have answered many of my questions on publishing. Once you've read through them read Writer Beware for good measure.
The wonderful people who operate these blogs and many more like them are the reason I know not to pay an agent (they take 15% once things are sold to a publisher and they don't get paid before that), that a good agent is worth every single bit of that 15%. Why it's worth taking my time and making the novel the very best it can be, and why unicorn stationary and glitter in a proposal are the bestest things ever!!! Yes I made that last bit up. Go forth and be educated.