If you're main objective for writing anything, especially books is to
 get rich, you may want to rethink your strategy. There are really only 
two good reasons to write 1) because you love to do so, 2) because you 
have something interesting, important, funny, scary (you fill in the 
word) that you want/need to share with the world. Then no matter what 
you do, you will be rich, because you will be fulfilled. But monetary 
riches may be slow to follow.
Do people get rich 
writing? Of course, but not many. That's why you need another motivation
 and a good understanding of the way the real world works. It usually 
takes several years to get publishers interested in publishing a book 
(even with an agent).  JK Rowling of Harry Potter fame was rejected 
numerous times over several years before interesting a publisher in 
Harry Potter (and her first advance was a measly 1500 pounds). Likewise,
 Wizard of Oz by L. Frank Baum was rejected over 100 times. Publishers 
said no one would believe in a fairytale set in America!
Granted
 both of the former examples are works of fiction, but writing 
non-fiction doesn't have significantly better odds of getting published 
any quicker than fiction. The only exception is if you have impeccable 
timing and just happen to write something just as related current event 
takes place. But even that is a very long shot.
I write
 these things to inform and prepare hopeful writers. You will need more 
than a little dose of determination to make a go of it. Here's the break
 down:
It often takes 1-10 years of searching, 
submitting, pitching, and repitching to get a publisher interested in 
publishing a book. Once that happens the traditional length of time from
 signing a publishing contract to seeing your book in a book store is 2 
years.
While there are exceptions to the 
rule, most publishers offer somewhere between 2k and 10k advances and 
2-10 percent of royalties. There is no absolute standard, everybody does
 it a little differently. It really depends on what you negotiate. But 
keep in mind the days of 50k or 100k plus advances are gone for all but 
the JK Rowlings and Stephen Kings are gone. 
The best 
advice I can give is to examine why you want to write. Then ask yourself
 how truly committed you are to the project? If the answer is more than 
anything, go for it. If it borders on I could take it or leave it, 
writing a book is probably not for you.
Remember the 
richest rewards of writing is in the enjoyment of the process and 
knowing you shared your story. Everything else is icing on the cake.
 
 
