(1) Be open to meeting everyone. You never know who you will meet...and there is potential for everything from dates to business partnerships to friendships. Also, don't forget that the person across from you might not be your ideal mate, but his/her best friend may be perfect for you.
(2) Don't get attached to the results. If you start the evening thinking you will get the most matches - you won't. It's not a competition. More importantly, the people meeting you will know that you are trying too hard and they will feel uncomfortable. Instead, expect to have a fun evening...and let the matches fall where they may.
(3) Prepare good questions. Avoid asking "what do you do for a living" and "where do you live." We all tend to ask these questions first, but what do they really tell you about the person you're meeting? Start here and your 5 minutes will be over before you know it. Alternatively, think of a couple of questions that will give you insights into common interests or will tell you about the person - for example: "what was the last book you read (movie you saw, CD you bought, etc)?" "where did you take your last vacation?" "where are you from?" "if you could travel anywhere in the world, where would it be?"