The prior answers are fine as far as they go, but maybe address substance as well as form? You are putting yourself out there for a reason and it is not for the small talk or facial recognition. You are there to network and protect your future or you would just soak up the academic content of the presentations and go back to planning your first IPO. This is a total package we are discussing.
Before approaching anyone, know what are you asking for and what you have to offer in return? When starting a career you are beginning a long-haul cold-calling sales job and the product is you. Times are tough and new grad working cash register to make ends meet (or even abandoning a career) has become a sick cliche now that technical jobs can be instantly exported to the lowest bidder overseas regardless of which continent you happen to be standing on.
Your opening salvo is a crowbar to get your foot in the door. Your crowbar will be seen as such so keep it friendly and subtle. Be prepared with a business card and a thirty-second speech, or a C.V. (and maybe a thesis) on a USB stick for a good prospect, or a short discussion of your interests and the potential business venture you are considering, or the current football score if all else fails. You want them to have a good impression of your professionalism and you want them to relate their own experiences to yours.
Professional conferences can be fun but not like the more casual atmosphere college students experience on campus, not even at an academic conference on campus. Professional decorum is mandatory (even in Silicon Valley).
As you work the room, track your performance mentally in real time, or better yet, also in a notebook offline, and hone your networking tactics and strategy based on your results. If you are not paying attention you could repeat the same mistakes forever. For best results you want people to like, respect, and maybe fear you as a potential competitor a little in order to capture their attention, and what you want them to remember about you is how they can benefit from knowing you.
In this modern era of the revolving door through government and rampant legal corruption of politics with corporate money, the 'little guy' is a splat waiting to happen (even in academia). Be aware that powerful hidden forces are moving through the room. The higher up the ladder those you reach out to, the more powerful those forces, and they might not have your welfare at heart. Think Hollywood drama on steroids without the fiction.
The way people respond is highly dependent upon your personal appearance. This affects everyone regardless of sex or attractiveness. If your appearance has built-in clash due to poor sense of image, you will not be taken seriously no matter how good your pitch is or how much your clothes cost. Think frumpy little old lady in bright red lipstick and flowered hat with a bow versus sleek professional model. Tart yourself up appropriately and people will respond better to you. Your investment will pay off as you avoid wasting money on apparel that hang in your closet forever unused.
You can buy your way into a professional look with an image consultant, but you can also learn it for free from books. In this discipline people are classified by 'season' (spring, summer, fall, winter) according to bone structure, geometry, coloring, and personality etc. It is purely an abstract concept that has nothing to do with the weather but rather how people as products of nature tend to reflect the traits found in nature. Everyone has a unique set of colors, textures, shapes, patterns, and style that 'harmonize' with their body and personality. For example, a 'spring' has small symmetrical geometrical patters such as circles squares and triangles with small bone structure versus a 'fall' that has large irregular shapes and a strong bone structure and both tend toward greens and yellows as opposed to reds and blues. Image consultants are trained to recognize such characteristics and advise you on how to take advantage of your personal attributes.
If you develop a personal interest in someone, well, be careful. It could be the best time of your life or it could ruin you. Be sure you know the risks you are taking, and why, before committing yourself. Times change. Tomorrow your suspended sentence for drunk driving her home might force you out of your profession and your nude pictures on the Internet could ruin your life forever.
I know of no one who got anywhere without some rough patches. Dare to be bold and maybe it will pay off. Happy hunting.