The first thing most recruiters will look for is to see how your portfolio is geared towards the position you're applying for. Where do you want to see yourself? In Animation? Games? Live-Action? Are there specific companies you're aiming for? Are you a 2D or 3D artist? The more specific we can get, the better we can deconstruct what would go in your portfolio. It also depends on whether you want to be a generalist or a specialist and to what degree.
Becoming the Generalist
Most portfolios are centered around a story with element breakdowns that show the visual language and aesthetic. A portfolio typically contains: character development, prop & vehicle design, environment design and keyframes that pull all elements together. Those interested in sequencing/storyboarding will have boards as the bulk of their portfolio. It would be helpful to title and label your images, characters, specific details, etc to show the thinking and decisions that went into the final product. An introductory paragraph that gives the premise of the project can not only ground your intention with your designs, but can also allow your audience to follow along. The elements of your projects could be proportionally split say: characters 60%, props 30%, environments/keyframes 10%. It should be obvious to the audience by the majority of what fills your portfolio, where your concentration is. The focus should always be centered around design and how specific design elements support and enhance the story. Once you can discover your concentration, props for example, the portfolio becomes straight forward. There might be 2-3 different projects that show a variety of styles and design choices through props. A specialist portfolio knows specifically what they enjoy, it is their niche and this generally takes some time to develop the understanding. It can range from knowing your industry, knowing you enjoy illustrating characters, more specifically animation, to deciding 3D animation over 2D. A niche can constantly be defined and will allow us to understand our particular "style." We all start generally until we can understand ourselves and our crafts to further refine.
"The important thing to remember is that you are seeking to unify and consolidate your life's work so that it is working for you, not the other way around."
Becoming the Specialist
Honing your craft is your process of defining your niche. Whatever you're doing, it's either getting more and more specific and unique or more and more general/unspecified. The great thing about being general is that you're open to more opportunities but not necessarily as findable/recognizable/unique/fulfilling to you specifically and the balance of it all is how we showcase our portfolios. As you go about building and diversifying your skills/portfolio, see if you can notice any patterns that begin to emerge - things you like in one category, and things you don't like in another. As soon as you begin to develop a sense for what you bring to the table, what sets you apart in your particular industry and the broader marketplace, leverage that. For lack of a better term, this niche that you create will be uniquely yours. To the degree that you define and differentiate it to suit your specific strengths and inherent interests, it will serve to focus your attention and conserve your energy so that whatever you are asked to contribute to will naturally be in alignment with your talents, expertise, and general inclination. This effect is usually attributed to having a 'recognizable aesthetic', but can just as easily be a theme or subject matter that is used to develop into multiple styles.
The important thing to remember is that you are seeking to unify and consolidate your life's work so that it is working for you, not the other way around. It's a fluid process where the more you do the more you'll come to realize what works or doesn't work for you. Having a body of work online will allow your art to be accessible and shared more easily. Nowadays, it seems like a prerequisite to have at least a website or profile on an online community platform (ie: instagram or tumblr). As long as it's online it'll allow people to find you and from there you can start an email chain asking for advice from those you trust (even those in the industry). The artist community is forever a student/teacher back and forth relationship with most willing and even wanting to help. Don't take it personally if there isn't a reply, most people tend to be busy but if you can get into a habit of asking for help or clarity, you'll be building a web of knowledge to draw from. A portfolio can always be considered "in progress," very much like us. Although it can be frightening to share and open up to others, this process, when rooted for personal development, will generate a lot of feedback that allows us to see how we see ourselves, how others see us, and how to work towards aligning with where we want to go.