Do relax. Be yourself, be positive, you will come across more approachable...
Do dress to impress but keep in mind to wear something you feel comfortable in. It's not a fashion show.
Do maintain eye contact and show interest in the person sitting opposite you.
Do remember your manners - try not to yawn, belch or look bored.
Do fill out your Speeding Ticket as you go. You may think you have a good memory but it will become extremely foggy after so many speed dates.
Do use the break to talk to people, especially if there's someone you want to get to know better.
Do ask interesting but relative questions to your arena in life. No point in asking about traveling when you've never been on a plane.
Do ask open ended questions not with just yes/no answers, remember it should be a conversation rather than an interview.
Do be honest with yourself about whether you like a person or not. No point in putting someone as a match just because he looks like Brad Pitt.
Do flirt a little and pay genuine compliments but not too over the top as otherwise you will come across as a over eager.