@bambi 100 pages per book at least (non fiction) because everything less doesn't feel like a book for me. With small booklets, you risk disappointing your customers.
@ThopHayt This can be said about any business. If something is completely new, there's less competition = less quality. I know the time when people were able to make great money with cheap "How to books" with 10 pages. But with the time the competition has grown = high quality because everyone is trying to be the best. So if you don't have success, it just means that you're not meet the quality standard which is necessary to be successful. But what's the opportunity? Jumping on the next hot business where it's more easy to make money? To realize that it's no more easy after two years? But how would you become a master in any business to be able to make the big sums if you break it as soon as it becomes difficult? For me the books are not "another method" to make money and I can guarantee you that it's getting harder and harder with the time. For example: I bet that animated pictures for Kindle books are coming during the next years and ordinary eBooks won't sell so good anymore. Is it reason to give up because it's getting harder? No, I'll learn how to create such animated pictures even if it takes 3 months. I do whatever is necessary to do to be successful. I think that's the big difference: Most people would say: "If I have to learn how to create animated pictures I could also publish 10 books within this time to increase my income by $2.000/month." But I would leave this money on the table because I'm focusing on the highest quality whatever it takes. Such decision are the "extra mile" successful people are talking about.
@MatteoMatt You're on the right track. In the beginning it's more important to learn instead of publishing books. I know that this sounds stupid because you have the pressure to make money and it's only possible when you publish new books. But on the other hand you need a "quality standard" to earn anything. My advice: Figure out what points (on which you have an influence on) are important to sell a book on Amazon. There a just a had full of points eg. price, description, cover, keywords, look inside feature, author page and so on. Write down every point! Next you should learn about these points and use your knowledge for the next book. If you're still unhappy with the results you should reflect yourself and your book: "Hmmm, why is my book not selling? I've learned everything about keyword optimization during the last weeks. I watched tons videos about this point, read articels, talked to other people and so on. So I'm sure that my keywords are not the problem. Hmmm, but do I really know everything about how to write a description? I heard about emotional questions at the beginning. So if I'm not sure I should learn everything about it. If I do it just like I guess my results are based on luck but I know that success is based on the right decisions. So I should make sure that I'm doing it right." Next book you implement your new knowlage. If you're not happy with your results you can say: "I'm 100% sure that my keywords and my descriptions are perfect. Where could be the problem? Hmmm, my book prices are X.99. But why? Maybe X.98, X.95, X.90 are better prices. I don't know so I should learn everything about prices." And so on.
So you have to be honest to yourself and don't rely on what you think. Focus on what's working and necessary to be successful. If you don't know it you have to learn it because otherwise your results will be based on luck.
It's an
exclusion procedure and with time you'll do the things right. Then your success is just a logical consequence. Now think about you're three years in this game like me and have mastered all the basics perfectly. You're still learning and implementing other details which are pushing you far away from the earnings of an ordinary publisher. For example: Last month I've paid for the synchronization of my book trailers. I've paid a professional speaker $10 for 10 seconds. But such details only paying off if you master the basics. So it's nothing for a beginner. A beginner should focus on the basics to be able to make eg. $100/book, increase his quality to make $200/book and so on. The time will come when you're focusing on $1000+/book. And if you are able to provide such a high quality you could automate some processes to scale it up to publish 5 of these books/month instead of one. But a beginner (let's say he's able to make $50/book per month in average) can't scale it up and think that he'll make 10k/month with his next books. Your results are based on your quality and your quality is coupled to your knowledge. So if you don't know something - Learn it!
About CreateSpace: It's a sub company of Amazon. They're producing paperbacks on demand. No costs but it's a little bit harder to master in comparison to eBooks (eg. the formatting is more complex). On the other hand you can sell paperbacks for up to $20-25/unit IF you're able to provide the quality to sell in this price range.
EDIT:
Just another example. Let's say you want to produce a chair. You rip off the laminate in your living room, produce 4 feets with a diameter of 1 inch and give it a pink color bevause you like pink and you GUESS other people will also like it. And then you expecting sales?

But the minimum quality standard in this industry to make any sales is: oak wood, feets with a diameter of 2 inches and white color. But you're forcing to sell this pink chair. You focus on producing hundreds of these chairs because I've heard that this is a numbers game. But you fail. After one year you find out ....white is the color that customers love. Now you produce tons of white chairs and fail again because your still use your old laminate which is not the industry standard. You'll lose another year and at the end you'll give up and say: "Chairs are not selling. You can't expect to sell chairs in 2016."
No, you were just not able to reach the quality standard. You can't focus on selling tons of chairs and expect to get rich if you don't have the knowledge how to produce proper chairs.
Nothing else for other businesses: You can't create a perfect book and thought: "The cover doesn't matter. I'll create it with MS pain. I think my keywords are okay" and expect any sales. It's nearly impossible or just luck if you get a sale. It doesn't matter what you think. You have to do what's necessary to do to be successful. And a bad cover, random keywords, generic title and so on doesn't meet the quality standard on Amazon to make any sales. So if your books are not selling, it's not because this business is dead (customers are already there, more than before) but because you missed sonething that's necessary. So there's no reason to keep on and force sales because you'll just repeat your bad results. Be honest to yourself, figure out what's the problem, learn about it even if you have to read 10 books for the next weeks, publish your next book, reflect yourself again, find the problem, publish the next book and so on. That's the only way