A good question to ask yourself when putting together a photo book portfolio is, how many photo's should you be using? This is an important aspect of the entire process whether this is you first portfolio or not. A few things to keep in mind here when considering this, is how important are the photographs in regard to conveying your message. As a professional photographer you are going to be experiencing different stages in your career, ranging from novice to highly experienced. As a novice you might want to consider showing off your best works that range widely in variety. Nature shots, cityscapes, indoor and outdoor shots, taken under a variety of lighting conditions, should all be displayed. If you have an eye for detail in any of the aforementioned styles, by all means accentuate that style by including that more than the other selections you present.
The message here is that you are not only showing off the variety of your photos, but also showing off your attention to detail and your love for the art of photography. In all, no less than 10 photographs should be displayed, and those 10 should represent the best of everything you have. If you are a professional with many years in the game and you are simply updating your portfolio, try not to use more than 30 of your best works. You don't want to overwhelm the viewer with images, but you also want them to know just how much experience you really have.
When using your best work, it is important to use the photographs that best showcase your talents in a quallity photo book. You don't really want to include any "lucky" shots that came along, as you know that it may not be possible to give someone photographs of that nature on a consistent basis. Be honest with yourself, as to where your natural talents lay, and convey that honesty to whomever you are going to be presenting your portfolio to. You are going to have anywhere between 10 and 30 photographs in your portfolio that you are going to be showcasing, so choose them wisely. This portfolio could very well launch you into the next phase of your career. A career that is not only lucrative, but fulfilling as well.