There is no recipe by which you can make a perfect design portfolio. This is a creative profession, therefore, to present their work too, using a creative approach. It can manifest itself in design, in the choice of work or something else, but in any case, nice looking portfolio always attracts attention.
For your portfolio choose your best work. Let them be not too much, but each of them you should be proud of. If works a little (it happens in novice designers) and you decide to dilute the best work middle, place most of the good work at the beginning and at the end, in the middle alternate.
If you do design for a long time, then near work select dates. This will help the employer or the client to evaluate your work experience and understand that you are an experienced person.
Take care of the structuring of the portfolio. The work done in different categories, it is better to break into subsections. Each subsection also you can sort them if you see fit to do it. Works that you take the trouble to write a brief description will be given far more attention.
If your work is complex (for example, web design with its own independent graphics and layout), not bad to clarify, what tools you used. So, you will demonstrate the skills of the various programmes in practice.
Those of your works that are used by customers, should be referenced. For example, today, whatever design you do, it will somehow be present in the Internet. This can be a design website, corporate style or logo or even pictures of objects created according to your sketches. It is useful to add links to live examples of their work to clients and employers can see that your design "works" and looks great in the incarnation.
Most likely, you work in different styles because these are features of the market: even if the designer likes to draw blue triangles, the customer sometimes wants to see the red squares. Here you have to make a choice: to show a portfolio of work in your favorite style or you can post as many different. If all you show, is your favorite style, it increases the chance to find an employer or customer from whom you will do exactly these things. On the other hand, the presence of works in a variety of styles, too, can be a good strategy, so you will never be without work. Customers and employers will see that you know everything, so you can be entrusted with any work.