Select only strong pictures
If you don't think that the picture is good enough, then do not include it to your portfolio. Do not include amateurish photos or over edited pictures. Get your friends or other's opinion about the pictures.
Include relevant shots
There are at least 6 important shots that you should include in your portfolio. Casual head shot, styled head shot, fashion shot, moving shot, catalogue shot, editorial shot, and a body shot.
Show variety
Make sure you have photos in landscape and in portrait. Include at least one black and white and one colored. The portfolio should give an idea of how you will look like given various circumstances.
Right choice of clothes and accessories
A good portfolio contains pictures that gives emphasis to the model. Remember its about you and not the clothes and the jewelries you are wearing, make sure that it does not take the attention from you.
Keep it less but with great quality
Do not include 2 photos from the same shoot or wearing the same clothes, get assistance from a professional if you can have their service for free or ask a knowledgeable friend to do some editing if necessary.
Neat compilation
Just like a resume your photos have to be professionally presentable, no loose photos, no cut up contact sheets, no loose slides, no torn or bent photos.
Keep on updating
As you gain experience you get more beautiful pictures. Add latest pictures or use it as a replacement for your older photos.