Being punctual doesn't mean arriving exactly at the time of the meeting; it's arriving at least 15 minutes earlier. This allows you to settle in and do a little pre-preparation for the meeting.
The way in which you dress can say a lot about you. In a professional environment make sure to dress accordingly. Ensure your outfit is clean without any stains or dirt on it, ironed, neat, and appropriate.
Start by introducing your name and position clearly, and if you're present with another colleague introduce them as well. Don't curse or speak obscenely, and remember to speak kindly of others.
Truly engage in the conversation you're having. Don't fiddle with your gadgets, turn them off if needed. Maintain eye contact and respond appropriately. Do not interrupt when they are speaking.
Some people are generally very touchy-feely when they converse, in a business meeting a handshake is as far as you go. Remember this is a professional setting not a casual one.
Business meetings usually involve food and beverages. Make sure to pace yourself with food and most definitely know your limit with alcohol. The last thing you want is to make a fool of yourself with your potential clients watching.
On the surface these practises seem like no brainers, but you'd be surprised as to how easily people forget them. Just remember that business meetings are to network, you should always maintain a certain sense of professionalism.
Be punctual
Dress accordingly
Mind the way you speak
Be interested in what is said
Be aware of your body language
Handle your food and beverages