...and a few things some people seem to not manage to learn.
1. You do not pay your publisher. Unless you are self publishing (in which case you pay your editor, your cover artist and your printer or ebook converter), you do not pay your publisher. Using a publishing service such as Lulu or CreateSpace makes sense for some...most especially niche non-fiction intended for back of the room sales. If you have a wider platform, it does not. A publisher you pay has absolutely no incentive to make your book a success; they already have their money.
2. No, Virginia, you do not get to design your own cover art. No, you cannot hire your second cousin or best friend to do your cover art. Your publisher will hire somebody who they know is good at it. You might get some say or even a veto, but ultimately, this is not something you can control.
3. Yes. Your publisher might change the title of your book. There are all kinds of reasons why they might (and often do) make that decision. Maybe there's a similar book coming out with a similar title. Maybe your title just sucks (I know some of mine do). Short stories are rarely re-titled, but it has happened to me. This does not mean you can get lazy and submit under a bad title, but you have to be aware that it might change...sometimes more than once.
4. Uh oh. You did not know Minor Character X had the same name as Minor Celebrity Y. Sometimes legal will come back and ask that the name of a character be changed. If you are really fond of a name, google it before submitting...then you'll have longer to get used to the idea that that name is not going to work.
5. No, you can't just sit back and let the royalties roll in. You do need to actively promote your book. That might involve a signing every weekend for the first few months. It might involve going to conventions for your genre. And you will, yes, need Facebook and Twitter accounts. You may find you need a professional Facebook account, not just a personal one. Oh, and you will need professional grade photos of you. Smiling into your webcam won't cut it. Get used to it. If you get stage fright, do something about it...join Toastmaster's, something, until you at least have it not affecting your performance. (Poetry jams can be great for practicing reading in public with a straight face and zero freak outs).
6. It is highly unlikely that you will ever be rich. Giving up the day job is relatively unusual. Many professional writers write non fiction to pay the bills. If you are dreaming about that million dollar movie deal...stop. What should matter is having readers not making money.
7. You will get rejected. You will get rejected a lot. You will be able to paper a room with rejections...and not necessarily the 'smallest room' either (although that might be the most appropriate). You may be told by an editor that your writing sucks and they don't think you can improve enough to ever be published. (Unprofessional, but I've seen it from people who should BE professional). An editor might send a rejection while drunk (also unprofessional, but wouldn't surprise me). You might get rejections that make you wonder which manuscript they read.
8. You will get bad reviews. You will get reviews that make you wonder what manuscript they read...or whether they were drunk. The temptation to tell the reviewer where to shove it can be very high. But remember...there is something worse than a bad review. No review.
Harsh reality checks, yes. But if you intend to be a writer, not just a hobbyist or wannabe, they need to be accepted...and even embraced.