If you're a newbie and haven't done a photo shoot before, you don't have to worry about that hurting your chances if you're looking for an agent to sign with. They love to sign undiscovered talent and will set you up with shoots for your portfolio right away.
If you are already modeling, then this post will most likely be more helpful to you but newer models can definitely take note as well!
The first thing your portfolio must do is reflect the type of work that you fit. In this particular case, only include images in your professional portfolio that you meet the requirements for. If you have an agent already, this will help them immediately submit you for bookings that are appropriate.
You do your agent no favor by being a 5'5" commercial/print model who only has high fashion images in your portfolio. That doesn't mean you can't do pictures that are outside of your field in the industry, because by all means you can, but when it comes to your agent and being considered for work, keep it to the themes your agency is representing you for.
If you are a commercial/print model, then your portfolio should contain that type of theme throughout. This goes for all parts of the industry. Of course there's no harm in including a little variety but make sure to communicate with your agent and get all of the photos you decide to put in your portfolio approved by your agent first.
In the age of online technology, many agencies now post online portfolios instead of having hard copies but you may still be required to have a portfolio book with printed hard copies of your images. This will definitely be the case for high fashion models. The ideal size for printing out your images is no bigger than 8"x 10". And make sure that you get a good quality, sturdy portfolio book or case that accomodates the size of your photos without wrinkling or tearing them.
Include no more than 20 photos. If you can, try to limit it to 15 photos. You never want to overwhelm the client with too many photos, unless your images are all stunning. Include both color and black and white images. If 15-20 photos sounds like it wouldn't be enough, keep in mind that over time models always update their portfolios with new shots so it's not like you'd be showing clients the same 15-20 pictures.
The most important thing to remember when it comes to your portfolio is to only include the BEST photos of you. EVERY SINGLE IMAGE IN YOUR PORTFOLIO SHOULD MAKE THE VIEWER GO "WOW"! Not, "okay", "cute", "nice", but "WOW". Each turn of the page should make them want to see more and ultimately, book you for their gig. Put your best photos on the right side of the portfolio book and the really good photos on the left side. This will allow them to catch your best images first and make them want to keep going through your book.
Never put an image in your portfolio that you have any doubts about. You need to be proud of your work and show your client and agent that you have what it takes to get the job done and that you are the one they should choose.